Migrate setup.cfg to pyproject.toml

[rsokl]

setup.cfg will be deprecated: pypa/setuptools#3214

iirc, we were opting for setup.cfg because it is what versioneer supports, but now they support pyproject.toml: python-versioneer/python-versioneer@dc6402f

possible conversion tool:
https://ini2toml.readthedocs.io/en/latest/readme.html

Note that pyright's config can now be placed in the pyproject.toml file: https://github.com/microsoft/pyright/blob/main/docs/configuration.md#sample-pyprojecttoml-file although there are some caveats that may make it not worth it: microsoft/pyright#694 (comment)