Enforce a consistent code style in pmbootstrap
Right now the pmbootstrap source code largely follows PEP-8 as far as I can tell, but we don't enforce it much apart from the few things Ruff complains about. I think it would be nice if we could enforce the code style via some formatter running in the CI. Personally I've had good experiences with Black, which nowadays is maintained under the Python Software Foundation namespace, so I think it is about as official as Python code formatters get.
One problem is that pmbootstrap's codebase currently does not conform to what Black wants entirely, so we would need to do some big commit that converts it all.