Use pyproject.toml instead of setup.py and setup.cfg where possible #356

Let's become more modern and update to use pyproject.toml instead of setup.py and setup.cfg. We'll probably still need setup.cfg, but let's move as much as we can to pyproject.toml.

We should also see if we can move other configuration such as .readthedocs.yml and .codecov.yml to pyproject.toml.

This relates mostly to PEP 621, and also to PEPs 518, 517, 660, and maybe others:

• https://peps.python.org/pep-0621/
• https://peps.python.org/pep-0518/
• https://peps.python.org/pep-0517/
• https://peps.python.org/pep-0660/

I labeled this as a "good first issue" if you're knowledgeable about such things or want to learn about it, since it's mostly about moving metadata from one format to another. This is a useful skill that I'm sure could be applied to many other projects as well!

These PEPs are largely about tooling for building packages and making metadata less programmatic. Since python-graphblas is pure Python and our releases, builds, and uploads are automated, we don't need to care that much about build tooling. What we care about with this is updating and centralizing metadata (i.e., PEP 621).

More context:

• https://www.shore.co.il/blog/pep-621-and-setuptools/
• http://ivory.idyll.org/blog/2021-transition-to-pyproject.toml-example.html
• https://snarky.ca/what-the-heck-is-pyproject-toml/