pyproject.toml for builds, using setuptools_scm for versioning

[markcampanelli]

Closes https://github.com/NREL/PVDegradationTools/issues/36

setuptools conversion reference: https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html

Refactor Notes

• Consolidates requirements.txt and many other config files into a single, standard, setuptools-based pyproject.toml.
• Replaces versioneer with setuptools_scm. Versions look similar to 0.1.dev506+g40c6f19.d20240110 when there are changes since last tag (e.g., while developing). Checking out a proper tag should produce the expected version string, so do this before building a distribution or documentation for release.
• pytest-runner is deprecated and was removed entirely, apparently without hurting anything.
• The test alias to pytest was dropped.
• I verified that the data files are being packaged, and pyproject.toml includes datafiles it finds by default, unlike older setup.py.
• Rebuilt the documentation with version added to upper left corner of main html page for documentation. (Not sure why a bunch of whitespace was added to several rst files.)
• Updated READMEs. Running locally with conda now exclusively suggests installing pvdeg using pip.

Release Notes

A project maintainer should try to upload this project to the test PyPI server to verify that resulting page looks ok (esp. parity with existing). I recommend using build to build the package tarball and wheel, e.g., python -m build . The resulting package should be universal. Usually, this is done after tagging, and, with the tag checked out, the dist artifacts will automatically pick up the version from git.

[markcampanelli]

@martin-springer Ready for review.

[markcampanelli]

Kewl. Glad this was found useful!