Streamline packaging configuration

[kafitzgerald]

Not at all a high priority item, but if we wanted to we could streamline the packaging a bit more to better leverage pyproject.toml and then remove requirements.txt (GitHub will pick up this info now from pyproject.toml) and setup.cfg.

[kafitzgerald]

This is overloading the issue a bit, but in streamlining / updating some of the packaging we could also address the use of some deprecated fields in our setup.cfg file.

See here:

• https://setuptools.pypa.io/en/latest/build_meta.html#dynamic-build-dependencies-and-other-build-meta-tweaks
• https://learn.scientific-python.org/development/guides/packaging-classic/#pep-517518-support-high-priority

It might also be good to look into this sooner rather than later.

I noticed it while working on dependency cleanup.