pyproject.toml pep 0517 and 0621

[foarsitter]

Upgrading to 3.12 required some changes in which dependencies are installed because setuptools is since 3.12 a hard dependency. I think it is a good idea to unify requirements.txt and test/requirements.txt into pyproject.toml (pep-621) and implement pep-517.

[greg-db]

Thanks! I'll ask the team to implement these.