Use release-only vcpkg triplet in sysio CI

[huangminghuang]

Summary

• Add a repo-local x64-linux-release vcpkg overlay triplet with VCPKG_BUILD_TYPE=release.
• Use the release-only triplet for both target and host vcpkg package builds in the reusable sysio build workflow.
• Pass ccache as the compiler launcher for CMake-based vcpkg ports, including LLVM when it has to compile.
• Include vcpkg-configuration.json and .github/vcpkg-triplets/** in the vcpkg binary cache key so cache entries are invalidated when registry or triplet behavior changes.

Why this is necessary

This mirrors the CI performance issue addressed in wire-cdt PR #55. wire-sysio already sets -DCMAKE_BUILD_TYPE=Release, but that only controls the top-level CMake build. vcpkg was still using the default x64-linux triplet, which does not set VCPKG_BUILD_TYPE, so package builds such as LLVM and protobuf can include unnecessary Debug variants or host helper packages under the default triplet.

Using x64-linux-release for both target and host triplets keeps vcpkg dependency builds release-only and makes the binary cache behavior more predictable.

Validation

• Parsed .github/workflows/build.yaml and .github/workflows/build_base.yaml with PyYAML.
• jq empty vcpkg.json vcpkg-configuration.json
• git diff --check
• vcpkg install --dry-run --x-manifest-root=. --triplet x64-linux-release --host-triplet x64-linux-release --overlay-triplets=.github/vcpkg-triplets shows LLVM, protobuf, and vcpkg helper packages selected under x64-linux-release.
• Isolated vcpkg package probe confirmed the overlay triplet passes -DCMAKE_C_COMPILER_LAUNCHER=ccache and -DCMAKE_CXX_COMPILER_LAUNCHER=ccache into CMake package configure, and the generated package CMakeCache.txt contains both launcher settings.

Notes

• This does not mark protobuf as host-only. Unlike CDT, sysio finds and links protobuf in normal target code paths, so protobuf remains a target dependency.