refactor(vmm): separate qemu launch concerns

[kvinwang]

Problem

vmm/src/app/qemu.rs mixed QEMU launch mechanics with unrelated responsibilities: VM workdir persistence, RPC presentation, application identity/measurement derivation, and host-share disk creation. VmConfig::config_qemu also interleaved host filesystem/probing side effects with a large block of command-line construction, which made the launch arguments difficult to test without a prepared host environment.

Fix

• move VM workdir layout and persisted state into workdir.rs
• move runtime-state aggregation and protobuf presentation into vm_info.rs
• move MAC/application identity and TDX/SNP measurement derivation into mr_config.rs
• move FAT32 host-share image creation into host_share.rs
• preserve the existing VmConfig and VmWorkDir re-exports for callers
• add PreparedQemuLaunch for disk creation, config reads, NUMA/TPM probing, and SNP capability detection
• add a decomposed QemuCommandBuilder for host-I/O-free QEMU argument construction
• add a unit test proving command construction works with nonexistent prepared paths

Verification

• cargo test -p dstack-vmm
• cargo clippy -p dstack-vmm --all-targets --all-features -- -D warnings
• ./run-tests.sh

[Copilot]

Pull request overview

Refactors dstack-vmm’s QEMU integration by separating VM workdir/state persistence, runtime info/protobuf presentation, measurement/app-identity derivation, and host-share image creation from QEMU launch preparation and command-line construction. This aims to make QEMU argument construction more testable and reduce host-side side effects in the command-building path.

Changes:

• Introduced workdir.rs for VM workdir layout + persisted state (manifest/state/paths, instance info, sys/app config accessors).
• Introduced vm_info.rs for aggregating runtime state into VmInfo and converting to protobuf for RPC.
• Split out measurement/app identity logic into mr_config.rs and host-share FAT disk creation into host_share.rs, while restructuring QEMU launch into PreparedQemuLaunch + QemuCommandBuilder (and adding a unit test for command construction with nonexistent paths).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
dstack/vmm/src/app/workdir.rs	New module encapsulating VM workdir paths and persisted state access.
dstack/vmm/src/app/vm_info.rs	New module for VM runtime info merging and RPC/protobuf presentation.
dstack/vmm/src/app/qemu.rs	Refactors QEMU launch into preparation vs command building; adds builder-focused unit test.
dstack/vmm/src/app/mr_config.rs	New module for MAC + TDX/SNP measurement/app identity derivation and persisted instance info updates.
dstack/vmm/src/app/host_share.rs	New module extracting FAT32 host-share disk image creation.
dstack/vmm/src/app.rs	Wires in new modules and updates re-exports/imports accordingly.

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