Fix flake8 errors

[mikemhenry]

Some notes:

1. I just removed the unused imports that it was complaining about
2. I fixed the line that was too long by breaking the comment into two lines
3. I told flake8 to ignore F401 (unused import) on __init__.py files (you can avoid this by using the __all__ = [foo, bar,] dunder but since we don't really export any api in the __init__.py that we would want to not pull in with a * import I opted to just ignore those checks on all __init__.py files)
4. I added the units it was complaining about to the "builtins" list -- I don't think there is a cleaner way of doing this in flake8. I am not sure how Literal[..] works but flake8 does something to make it work, we may be able to get FloatQuanity to do some magic to make it work the same.

We should make this a required check since when pre-commit fails we either need to fix the errors or tell pre-commit to ignore the error if it is a false positive.

If things have settled enough, all the CI, docs, and pre-commit.ci should be required IMHO

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.40%. Comparing base (da4b80b) to head (5aa6878).
Report is 4 commits behind head on main.

Additional details and impacted files

[mikemhenry]

Once you merge this in, you should be able to update the other PRs and that will fix pre-commit.ci on those PRs as well

[hannahbaumann]

Awesome, thanks @mikemhenry ! Lgtm!