Refactor/py pkg update

[saalUW]

Added:

• py-pkg format files (ruff, doc build, etc.) // pyDisagg specific info is missing
• pre-config.yaml file // current implementation means the user has to pip install pre-config and run in the pydisagg directory
• init file to age_split

Updated:

• init file
• build.yml // updated install and run steps, added filepath to ensure pydisagg venv is being called for the test
• pyproject // changed setup.cfg to match pyproject standards

Removed:

• setup.cfg / .py
• sphinx directory