Add arch-specific provider; remove PunchthroughProvider

[jaybosamiya-ms]

This PR removes the last vestiges of the PunchthroughProvider, moving out architecture-specific register management into its own trait. For now, I've only added support for x86-64's fsbase/gsbase, with platforms deciding which ones they'd like to support and which ones they do not want to support. This slightly expands beyond the only-fsbase behavior that existed in the old code, but acts as a way to improve clarity on usability (indeed, handling these generically will be needed if/when we want a proper WinNT shim, so might as well generalize right now).

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

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--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/enum_missing.ron

Failed in:
  enum litebox::platform::EitherError, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/mod.rs:209
  enum litebox::platform::trivial_providers::ImpossiblePunchthroughToken, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/trivial_providers.rs:48
  enum litebox::platform::trivial_providers::ImpossiblePunchthrough, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/trivial_providers.rs:40
  enum litebox::platform::PunchthroughError, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/mod.rs:198

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/struct_missing.ron

Failed in:
  struct litebox::platform::trivial_providers::IgnoredPunchthroughProvider, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/trivial_providers.rs:66
  struct litebox::platform::trivial_providers::IgnoredPunchthrough, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/trivial_providers.rs:77
  struct litebox::platform::trivial_providers::ImpossiblePunchthroughProvider, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/trivial_providers.rs:26
  struct litebox::platform::trivial_providers::IgnoredPunchthroughToken, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/trivial_providers.rs:85

--- failure trait_added_supertrait: non-sealed trait added new supertraits ---

Description:
A non-sealed trait added one or more supertraits, which breaks downstream implementations of the trait
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#generic-bounds-tighten
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/trait_added_supertrait.ron

Failed in:
  trait litebox::platform::Provider gained ArchSpecificProvider in file /home/runner/work/litebox/litebox/litebox/src/platform/mod.rs:29

--- failure trait_method_missing: pub trait method removed or renamed ---

Description:
A trait method is no longer callable, and may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-item-signature
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/trait_method_missing.ron

Failed in:
  method clear_guest_thread_local_storage of trait ThreadLocalStorageProvider, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/mod.rs:678

--- failure trait_missing: pub trait removed or renamed ---

Description:
A publicly-visible trait cannot be imported by its prior path. A `pub use` may have been removed, or the trait itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/trait_missing.ron

Failed in:
  trait litebox::platform::PunchthroughToken, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/mod.rs:173
  trait litebox::platform::PunchthroughProvider, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/mod.rs:156
  trait litebox::platform::Punchthrough, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox/src/platform/mod.rs:191

--- failure trait_removed_supertrait: supertrait removed or renamed ---

Description:
A supertrait was removed from a trait. Users of the trait can no longer assume it can also be used like its supertrait.
        ref: https://doc.rust-lang.org/reference/items/traits.html#supertraits
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/trait_removed_supertrait.ron

Failed in:
  supertrait litebox::platform::PunchthroughProvider of trait Provider in file /home/runner/work/litebox/litebox/litebox/src/platform/mod.rs:29

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/enum_missing.ron

Failed in:
  enum litebox_common_linux::PunchthroughSyscall, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox_common_linux/src/lib.rs:2662

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/struct_missing.ron

Failed in:
  struct litebox_common_linux::UserDescFlags, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox_common_linux/src/lib.rs:948
  struct litebox_common_linux::UserDesc, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox_common_linux/src/lib.rs:941

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/struct_missing.ron

Failed in:
  struct litebox_platform_linux_kernel::LinuxPunchthroughToken, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox_platform_linux_kernel/src/lib.rs:57

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/struct_missing.ron

Failed in:
  struct litebox_platform_linux_userland::PunchthroughToken, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox_platform_linux_userland/src/lib.rs:1196

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/struct_missing.ron

Failed in:
  struct litebox_platform_lvbs::LinuxPunchthroughToken, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/c6d47943dd9d45d7a9bc9ab6caef4e1969bca0fd/litebox_platform_lvbs/src/lib.rs:398