MNT: Apply ruff formatter

[greglucas]

Currently we use the ruff linter for style checks, but we don't have any explicit formatter. I'm proposing here that we also use the ruff formatter (drop-in replacement for black). I personally have learned to appreciate the opinionated auto-formatters because then as a reviewer I don't have to comment on minor formatting issues and as a coder I can just let the auto-formatter do its thing.

Most of the changes are single-quote to double-quote and adding a space after import lines / docstring lines. In general, I would say that most of the updates are improvements, there are a few that I maybe wouldn't have done but in my opinion that is OK and we can just let the formatter do its thing and handle the wrapping etc for us (they are still easy enough for a human to parse what goes where).