Move from `setuptools` to `uv`.

[CSchoel]

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The Python tooling ecosystem has involved considerably since I first created nolds. It's time to move to modern tools. Especially, the custom setup.py has to go in favor of a proper pyproject.toml. I also want to use uv for better dependency management over pip and setuptools.

• [x] Create pyproject.toml.
• [x] Copy all info from setup.py into pyproject.toml (or other respective files, such as MANIFEST.in).
  • [x] Dependencies
  • [x] Specify required versions for dependencies
  • [x] Extras
  • [x] Metadata
• [x] Test installation locally

[CSchoel]

Update: Forget poetry, we're going straight to uv, baby. 😁