ci: use native runner for Windows ARM64 releases

[meop]

Summary

• Run the existing aarch64-pc-windows-msvc release and test jobs on GitHub native windows-11-arm runners.
• Add the Windows ARM64 GNU-family Rust target, aarch64-pc-windows-gnullvm. Rust does not provide a literal aarch64-pc-windows-gnu target.
• Package every Windows target by target triple, so ARM64 binaries are archived as ZIP files with sd.exe.

Toolchain

The GNU-family target installs the MSYS2 CLANGARM64 toolchain and uses the setup action output for Cargo linker configuration. This avoids a runner-specific hard-coded path.

Validation

• Existing MSVC native-runner smoke: successful build and archive.
• GNU-family native-runner smoke: successful build, ZIP package, and artifact upload.

The fork-only validation workflow is not included in this PR.