fix(windows): restore MXC MSVC builds

[drew]

Summary

Restore the advisory Windows MSVC x64 and ARM64 lanes after two MXC compile regressions reached main.

Related Issue

No issue required: this is a localized compilation repair for existing CI coverage.

Changes

• update the MXC gRPC adapter to use the canonical compute-driver request name field
• make openshell-policy a normal MXC dependency because production policy mapping calls its enum helpers
• resolve Windows-only Clippy diagnostics, retaining a targeted allowance for the test that intentionally covers the legacy TLS enum variant

Testing

• cargo check -p openshell-driver-mxc --lib
• cargo test -p openshell-driver-mxc
• cargo clippy -p openshell-driver-mxc --all-targets -- -D warnings
• mise run pre-commit
• Windows MSVC x64 and ARM64 lint and test

Both native Windows architectures pass the full PR lint and test jobs. The seed-cache and binary-build jobs run only on main or manual dispatch and exercise the same corrected Windows-supported workspace compilation.

Checklist

• The changes are scoped to the Windows MXC compilation failures
• Conventional commits with DCO sign-off
• Relevant local checks pass
• Native Windows x64 and ARM64 checks pass