feat(fetch_azure): adapt fetch HttpClient to Azure's HttpClient

[martintmk]

Summary

Adds two crates that adapt Oxidizer building blocks to the Azure SDK abstractions, built directly on typespec_client_core 1.0.0 (the crate that defines the HttpClient and AsyncRuntime traits that azure_core re-exports):

• fetch_azure — AzureHttpClient implements typespec_client_core::http::HttpClient on top of a fetch::HttpClient transport.
• anyspawn_azure — Runtime implements typespec_client_core::async_runtime::AsyncRuntime on top of an anyspawn::Spawner (spawning) and a tick::Clock (sleeping). With the optional azure-identity feature it also implements azure_identity::Executor, running developer-credential commands on the spawner.

fetch is depended on without enabling any of its features.

Details

• AzureHttpClient converts a typespec Request (method, URI, headers, and bytes or seekable-stream body) into a fetch request, executes it, and maps the fetch response back into an AsyncRawResponse with a streamed body. Empty bodies and byte bodies avoid copies; non-UTF-8 response headers are skipped (matching the built-in reqwest transport). Build errors map to DataConversion; transport errors to Io.
• Conversions: From<fetch::HttpClient> and From<AzureHttpClient> into Arc<dyn HttpClient>; From<Runtime> into Arc<dyn AsyncRuntime>.
• Runtime spawns tasks wrapped in futures::future::Abortable so cancellation wakes pending waiters; sleep uses tick::Clock::delay.
• Examples: azure_transport (transport round-trip) and blob_list (transport + anyspawn_azure executor + DeveloperToolsCredential, listing blobs on tokio).
• Integration tests + doctests; client.rs and runtime.rs are each at 100% line/region coverage.

This mirrors the in-tree reqwest adapter shipped by typespec_client_core.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (963e015) to head (3438550).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #494    +/-   ##
=======================================
  Coverage   99.9%   100.0%            
=======================================
  Files        336      338     +2     
  Lines      24829    24932   +103     
=======================================
+ Hits       24818    24932   +114     
+ Misses        11        0    -11     

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[github-actions]

⚠️ Breaking Changes Detected

error: failed to retrieve local crate data from git revision

Caused by:
    0: failed to retrieve manifest file from git revision source
    1: possibly due to errors: [
         failed to parse /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/1f0b5970b95b02ee08d19ac3d38733fabb2e06f6/Cargo.toml: no `package` table,
         failed when reading /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/1f0b5970b95b02ee08d19ac3d38733fabb2e06f6/scripts/crate-template/Cargo.toml: TOML parse error at line 9, column 26
         |
       9 | keywords = ["oxidizer", {{CRATE_KEYWORDS}}]
         |                          ^
       missing key for inline table element, expected key
       : TOML parse error at line 9, column 26
         |
       9 | keywords = ["oxidizer", {{CRATE_KEYWORDS}}]
         |                          ^
       missing key for inline table element, expected key
       ,
       ]
    2: package `anyspawn_azure` not found in /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/1f0b5970b95b02ee08d19ac3d38733fabb2e06f6

Stack backtrace:
   0: anyhow::error::<impl anyhow::Error>::msg
   1: cargo_semver_checks::rustdoc_gen::RustdocFromProjectRoot::get_crate_source
   2: cargo_semver_checks::rustdoc_gen::StatefulRustdocGenerator<cargo_semver_checks::rustdoc_gen::CoupledState>::prepare_generator
   3: cargo_semver_checks::Check::check_release::{{closure}}
   4: cargo_semver_checks::Check::check_release
   5: cargo_semver_checks::exit_on_error
   6: cargo_semver_checks::main
   7: std::sys::backtrace::__rust_begin_short_backtrace
   8: main

If the breaking changes are intentional then everything is fine - this message is merely informative.

Remember to apply a version number bump with the correct severity when publishing a version with breaking changes (1.x.x -> 2.x.x or 0.1.x -> 0.2.x).