Ruff handles black, flake8 and isort in one package, and is way faster.
The isort rules had not been enforced, so this commit includes a lot
of import resorting changes.
I switched to flake8-bugbear and the standard black-compatible line
length of 80 + 10% (so max 88 characters), so some line reflowing is
included too.
Finally, because bugbear rightly points out that `setattr()` is less
performant, I've switched the `__signature__` assigment back to using
a direct assignment with type ignore comment.
