fixes #585
fixes #559

All changes are in place. Here's a summary of what was done:

Changes Made

1. ci-build-binary-artifacts.yaml

Fix 1 — Native arm64 runners:

• Added runner field to the CPU matrix: x86_64 → ubuntu-22.04, arm64 → ubuntu-22.04-arm
• Changed runs-on: ubuntu-22.04 → runs-on: ${{matrix.cpu.runner}}
• Removed Set up QEMU step entirely (not needed when each architecture runs on its own native runner)

Fix 2 — vcpkg binary cache:

• Added actions/cache@v4 step to restore/save ~/.cache/vcpkg/archives for all 6 Linux jobs (keyed by pkg-type + arch + vcpkg.json hash)
• Added the same for macOS (~/Library/Caches/vcpkg/archives)
• Fixed Docker GHA layer cache to use per-job scope to avoid the 6 matrix jobs thrashing each other's cache

2. All 6 docker-build-{type}-{arch}.sh scripts

• Added mkdir -p $HOME/.cache/vcpkg/archives before docker run
• Added -v $HOME/.cache/vcpkg/archives:/root/.cache/vcpkg/archives volume mount so vcpkg inside the container reads/writes the cache restored by actions/cache on the runner host

Expected result: On the next tag push, protobuf:arm64-linux should build in minutes on the native arm64 runner (vs 3.2 hours under QEMU), and subsequent runs will skip rebuilding already-cached packages entirely.