feat: add setup-vcpkg composite action with binary caching

[CameronBrooks11]

Summary

Adds a shared composite action at .github/actions/setup-vcpkg/action.yml that replaces lukka/run-vcpkg across the org.

Why

lukka/run-vcpkg@v11 sets VCPKG_BINARY_SOURCES=clear;x-gha,readwrite, but vcpkg removed the x-gha provider in April 2025 (microsoft/vcpkg-tool#1662). The clear also disables the default filesystem cache. Result: every CI run compiles all vcpkg packages from source — gRPC alone takes 33–46 minutes.

This affects all 5 C++ repos in the org (provider-sim: 2h50m, anolis: 2h, fluxgraph: 50m, bread/ezo: 22m).

What this action does

1. Clones vcpkg at a pinned commit (shallow, filter=blob:none)
2. Bootstraps (bootstrap-vcpkg.sh on Linux, .bat on Windows)
3. Sets VCPKG_ROOT and VCPKG_BINARY_SOURCES=clear;files,...,readwrite
4. Restores/saves binary cache via actions/cache@v4

Usage (for consuming repos)

- name: Setup vcpkg
  uses: anolishq/.github/.github/actions/setup-vcpkg@main
  with:
    vcpkg-commit: ${{ env.VCPKG_COMMIT }}
    triplet: x64-linux-static

Testing

Self-test job added: installs yaml-cpp on both Linux and Windows, verifies binary package appears in cache directory.

Rollout plan

1. This PR (Phase 0) — validate action works
2. Phase 1: Apply to anolis-provider-bread (simplest repo)
3. Phase 2: Roll out to ezo → fluxgraph → anolis → provider-sim

References

• [vcpkg-tool] cache fail in GHA microsoft/vcpkg#45073 — cache fail in GHA (still open)
• why run-vcpkg Is missing out on x-gha cache: it has been removed from vcpkg lukka/run-vcpkg#251 — x-gha removed (still open)
• Remove x-gha binary cache provider microsoft/vcpkg-tool#1662 — PR that removed x-gha