Apply preview ruff rules

[DimitriPapadopoulos]

Fix issues reported by ruff check --preview.

I have no experience using asyncio, so I am not confident in the RUF029 fixes.

TODO:

• [ ] Add unit tests and/or doctests in docstrings
• [ ] Add docstrings and API docs for any new/modified user-facing classes and functions
• [ ] New/modified features documented in docs/tutorial.rst
• [ ] Changes documented in docs/release.rst
• [x] GitHub Actions have all passed
• [x] Test coverage is 100% (Codecov passes)