Add black style check on lint

[camenpihor]

fix #221

Changes

1. I noticed that we say the library uses the black code style in the readme, and that the code is already black-ified so I added a black check to the lint script
   • I excluded tests from the check, because of personal preference, but happy to run the black checker on the tests too, if you want? (although they don't pass right now)
   • I think the code was already set to line length 100, so I used that, but happy for this to be whatever (I use 90 personally)
2. Call the lint script from the test script

[canyon289]

This just installs black. Is it intended that a check will be performed as well?

Nevermind: I see it, for some reason github didn't load full diff when I checked :)

[canyon289]

Id say include tests because inevitably someone will end up running black on tests and itll obscure the git blame path, and also because why not, but not super strongly opinionated about it

[camenpihor]

Thanks for the review! I'll merge after tests pass