Work items for package, build and test improvements

[aaronj0]

Consolidate tests as

• Folder containing C++ sources that are built as shared libs that are loaded
• Folder containing pytest .py files
• Folder containing test utils

CI Test Reporting [compiler-research-ghactions-bot]:

• One big comment containing [CI, Codecov, Benchmarks]. comment system modified, CI test and benchmark runs have history retention, inverted stack that has collapsed history, and displays latest stats (with hashes).
• CI workflows can consolidate this across all compiler research repositories

Dead code removal:

• Analyse codebase for stale function paths and remove them

Clang-Tidy

Automatic PR branch name synchronisation in testing across both repositories. Editing the yaml with remote and branch ref should be an override. Cppjit cmake, specifies the last supported CppInterOp hash. If the users PR's base commit is ahead of that, then do not run CI.