feat(vmm): add static configuration validation

[kvinwang]

Summary

Add a side-effect-free check-config command for validating static configuration invariants.

The extended checks run only when check-config is explicitly requested, so existing serve and run behavior is unchanged. The pre-existing host API validation remains part of normal startup.

Validation performed

• Require a valid vsock:<cid> host API address and a nonzero host API port.
• Parse the Rocket management API address and port.
• Validate the guest CID pool bounds and prevent range overflow.
• Restrict host share mode to 9p, vhd, or vvfat.
• Reject zero enabled auto-restart intervals and reversed port-mapping ranges.
• Validate MAC prefixes and mode-specific bridge/custom networking fields.
• Reject empty required Supervisor paths and an empty executable when auto-start is enabled.
• Require KMS, Gateway, PCCS, and NVIDIA proxy endpoints to be valid HTTP(S) URLs with hosts.

The checks are intentionally limited to static invariants. They do not access external services, require host devices, or mutate host state.

Usage

dstack-vmm --config /etc/dstack-vmm.toml check-config

A valid configuration prints configuration is valid; an invalid one exits with an error.

Tests

• cargo test --manifest-path dstack/Cargo.toml -p dstack-vmm config::tests::
• cargo check --manifest-path dstack/Cargo.toml -p dstack-vmm
• cargo fmt --manifest-path dstack/Cargo.toml --all
• git diff --check

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.