CI: It's impossible to add file docstrings

It's impossible to add docstrings to the top of Python files in Nephthys.

This is because our pre-commit hooks include:
- `reorder-python-imports`, which _removes_ any newlines in between a docstring and imports
- `ruff-format`, which _adds_ a newline in between the docstring and imports

Upstream issues are https://github.com/asottile/reorder-python-imports/issues/366 and https://github.com/psf/black/issues/4175, but neither project is interested in fixing compatibility.

Switching to `isort` ([with the config suggested in a GH comment](https://github.com/psf/black/issues/4175#issuecomment-1915522848)) might be a way to resolve this conflict.

We don't have any file docstrings at the moment, so it's not an important issue, but definitely worth documenting and probably fixing _at some point_