new: enable black, isort, flake8, mypy

[aMahanna]

Re-enables linting & type-checking.

We'll eventually switch to using ruff

Additional notes:

• Minor code cleanup, function & variable renaming
• Some unused code was removed, which was originally brought over from nx-cugraph
• Any and type: ignore were generously used as a first pass. NetworkX is untyped, so had to compromise on certain parts.