Require that Python code conform to the Black formatter

[anshumanmohan]

Let's expand the scope of mandatory Black formatting in CI. Currently only two directories are tested, but I think this can safely be expanded to include all of calyx-py for instance.

Right now if I run black calyx-py I get

am3327@havarti:/scratch/anshuman/calyx$ black calyx-py/
...
All done! ✨ 🍰 ✨
22 files reformatted, 32 files left unchanged.

@polybeandip interested? Since it bit you once before and you figured this out in OCaml-land recently?

[polybeandip]

Happy to set up the github action for this