PEP 621: Migrate from setup.py to pyproject.toml

[cclauss]

Closes #2409
Closes #2431

• Update setup.py to accommodate Python3.13.0 #2409
• setup.py: Remove deprecated pkg_resources in favor of importlib.util #2431

Running on Python 3.13 is currently blocked by numba.

Why

https://setuptools.pypa.io/en/latest/userguide/quickstart.html#setuppy-discouraged

https://setuptools.pypa.io/en/latest/userguide/quickstart.html

We recommend users expose as much as possible configuration in a more declarative way via the pyproject.toml or setup.cfg, and keep the setup.py minimal with only the dynamic parts (or even omit it completely if applicable).

From validate-pyproject README:

With the approval of PEP 517 and PEP 518, the Python community shifted towards a strong focus on standardization for packaging software, which allows more freedom when choosing tools during development and make sure packages created using different technologies can interoperate without the need for custom installation procedures.

This shift became even more clear when PEP 621 was also approved, as a standardized way of specifying project metadata and dependencies.

validate-pyproject was born in this context, with the mission of validating pyproject.toml files and ensuring they comply with the standards and PEPs.

https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#writing-pyproject-toml

git checkout -b setup.py-to-pyproject.toml
pipx run setuptools-py2cfg setup.py > setup.cfg
pipx run 'ini2toml[full]' setup.cfg -o pyproject.toml
git add pyproject.toml
git rm setup.py
rm setup.cfg
pipx run pyproject-fmt pyproject.toml
pipx run 'validate-pyproject[all]' pyproject.toml
git commit -am"PEP 621: Migrate from setup.py to pyproject.toml"
git push

After this PR is merged, requirements.txt could be deleted.