Standardize test conventions and modernize docstring/lint tooling

[sou-cheng-choi]

1. Renamed/replaced following the test_<area>_<topic>.py convention.
2. Restructured test files to object classes if necessary.
3. Implemented style gate scripts (check_test_style.py, check_docstring.py) to enforce strict filename and Google-style docstring conventions.
4. Updated the CI system (Makefile, alltests.yml) to strictly gate Pull Requests (PRs) on these new style checks.
5. Standardized documentation checks by integrating pydoclint into pyproject.toml and the build process.
6. Added new documentation guidelines inCONTRIBUTING.md, docs/good_practices.md, and docs/tests.md.
7. Removed (again) qmcpy/accumulate_data/__init__.py as it is dead code.

[fjhickernell]

Thanks, Sou-Cheng. I am curious. What if a test spans two areas, e.g., stopping criterion and kernel?

[sou-cheng-choi]

@fjhickernell

There is a label called "ee" for end-to-end tests. This is one option. Another option is to choose the primary category of the two.

I have made a commit to clarify the issue.