MAINT: Migrate to PEP517/518 packaging

[esavary]

• Migration of package build to PEP 517/518 standards.
• Transition packaging from setuptools to hatch.
  closes Migrate packaging to PEP517/8 #127

[effigies]

Apologies for spinning this out. It kind of became one thing after another, as the installation shows up in several places that weren't being tested properly.

This now:

1. Moves to hatch/hatch-vcs.
2. Updates CI in various places and ensures docs build on PRs.
3. Fixes doc build and lint issues.
4. Tests up to Python 3.12, which was probably an overreach, but I was in there already.

[effigies]

This is ready to go AFAIC.

[oesteban]

Just added two minimal comments, which came from the fact that I gave a probably not-ideal example reference PR with sdcflows.

[oesteban]

Please feel free to merge when you're ready @esavary

[oesteban]

I'm not sure this change will work -- let's keep an eye on this. I remember pinning furo because of some weird dependency failing in more recent builds. Perhaps they figured out.

[effigies]

I built it locally.