Draft: Use Black instead of YAPF

Since the flake8 pre-commit hook finds a lot of pep8 violations when run on everything (pre-commit run -a), if checked out how the situation would be with black. This fixes all but one of the pep8 errors and generally drives down the error count from 123 to 37. IMO we either need to update/fix the yapf config to produce pep8 compliance (which might not be possible) or just go with black. Since we're also using notebooks now, there's nb_black to consider too. Afaics yapf has no notebook support, nor is there a sister project like with nb_black