Add pre-commit.ci

[mikemhenry]

I've been using https://pre-commit.ci/ on a few projects now and really like it. It allows me to offload linting and formatting to a different service and then use GHA for unit testing. This uses pre-commit hooks but doesn't require develops to setup hooks locally, which means it is one less thing to configure, but because pre-commit can commit, that means instead of CI failing because of an error that black can fix, the fix just happens. This also makes it easier to accept contributions from new people, since they have less to setup and auto-formatters can just fix the code.