Replace setup.py and requirements.txt with poetry or rye

[shrik450]

Since we're consolidating everything into pyproject.toml anyway, we should consider switching to poetry. We'd be able to track all of our dependencies in pyproject.toml instead of requirements.txt and requirements-test.txt, use poetry's convenience features instead of having to manually manage venvs and using pip install --editable. The biggest advantage of this is that we'd no longer have to rely on setup.py.

Another option is rye, which is by the same co behind ruff, and bundles ruff. This would help us unify our CI completely. Rye is currently pre-1.0, which may be a concern.

(This is not a currently pressing concern, but there are minor inconveniences involved with setup.py and pip right now which can be vastly simplified.)