MNT: remove setup.cfg

[neutrinoceros]

• MNT: move versioneer configuration to pyproject.toml
• CLN: drop unused pytest configuration from setup.cfg
• MNT: rename setup.cfg -> .flake8

[rgommers]

Why is the pytest config unused? A quick skim of the docs says it's picked up: https://docs.pytest.org/en/7.1.x/reference/customize.html#setup-cfg

I'd put it in pytest.ini normally, but it does seem to be doing something.

[rdbisme]

Maybe we want to decide if we want all things possile into pyproject.toml or in separate files. I'm more to go all in pyproject.toml (and move from flake8 to ruff)

[neutrinoceros]

Pytest doesn't compose configuration. pyproject.toml takes precedence over setup.cfg, so it's effectively ignored.

[neutrinoceros]

and move from flake8 to ruff

Happy to contribute this too in another PR