[CI] Cache vcpkg to improve GitHub Actions performance

[kox13]

Issue

CI pipeline for the Agent project is slower than necessary due to repeated downloading and rebuilding of dependencies managed by vcpkg.

Currently, each workflow run may:

• re-fetch dependencies from scratch
• recompile installed packages
• not reuse previously built artifacts

This results in unnecessary CI execution time, especially for dependency-heavy builds.

Suggestion

Introduce caching for vcpkg artifacts in GitHub Actions via cache key based on: OS, vcpkg.json / dependency manifest hash