Rust Protocol Metadata Source

Minimal GitHub Actions pipeline that publishes rust-versions-public.json for each new Rust server build.

What it does:

• Web pre-check (api.steamcmd.net) to read current build_id/manifest_id.
• Skips heavy work if build_id matches the latest release asset.
• Downloads Rust.Global.dll, extracts protocol via tools/RustProtocolProbe, and publishes a new GitHub release asset.

Scope is intentionally narrow: Rust build + protocol only.