Build cache on commits to base using proper cache keys.
Use fresh cache during CI builds (big improvement to build times).
Skip clang-tidy if no source changes during CI builds.
Improve CI results using GitHub Actions summaries.
Move CI test job into separate workflow.
Combine Windows and Linux test workflows.
Note:
ccache cache isn't being extracted from Docker image, causing full
rebuilds every time. Disable Docker build in CI workflows until we can
fix this.
