feat: use more powerful machines for building Windows releases

[bolinfest]

Windows release builds in .github/workflows/rust-release.yml were still using GitHub-hosted windows-latest and windows-11-arm runners. This change aligns release builds with the faster dedicated Codex runner pool already used in CI, and adds machine-spec logging at startup so runner capacity (CPU/RAM/disk) is visible in build logs.

What Changed

• Updated the build job to support matrix entries that provide a full runs_on object:
  • runs-on: ${{ matrix.runs_on || matrix.runner }}
• Switched Windows release matrix entries to Codex runners:
  • windows-latest -> windows-x64 with:
    • group: codex-runners
    • labels: codex-windows-x64
  • windows-11-arm -> windows-arm64 with:
    • group: codex-runners
    • labels: codex-windows-arm64
• Updated the ARM-specific zstd install condition to match the new runner id:
  • matrix.runner == 'windows-arm64'
• Added early platform-specific runner diagnostics steps (Linux/macOS/Windows) that print OS, CPU, logical CPU count, total RAM, and disk usage.