Add Nox session that uses autotyping to automatically add type hint annotations

[namurphy]

This PR adds the autotyping session to noxfile.py ✨, along with some mypy troubleshooting information that gets printed out when mypy runs.

This session provides two autotyping options so far:

• safe: which will add type hints that have a very high probability of being correct
• aggressive: which will add type hints that will usually be correct but sometimes may not be. Since using this option will necessitate a careful code review, it should never be used in CI.

📌 In the not-too-distant future, I'd like to either add this to our CI, or provide better instructions for contributors on how to use this. Alternatively, we could run this with the safe option as a pre-commit hook, which would let contributors add type hints to PRs with pre-commit.ci autofix comments. I'm hoping this will make adding type hints easier.

🌠 We could also add rules where if a variable is named B, then a type hint of u.Quantity[u.B] gets automatically added, but I'll save that for a standalone PR.

📝 A limitation of autotyping is that it will only add simple type hints rather than more complicated ones. We could potentially also add a Nox session for other tools like monkeytype which will run pytest and then apply type hints based on the type hints found at runtime. We wouldn't be able to include that in CI because changes from those tools will require careful code review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.14%. Comparing base (c39ccee) to head (991f441).

Additional details and impacted files

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  Coverage   95.14%   95.14%           
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  Files         107      107           
  Lines        9411     9411           
  Branches     2168     2168           
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  Hits         8954     8954           
  Misses        276      276           
  Partials      181      181           

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[namurphy]

Fortunately this particular emoji shows up nicely in the output of GitHub Actions! I expect that it'll be useful to draw people's attention to the troubleshooting information.

[namurphy]

After the changes from autotyping, mypy found that the run method here was returning None, which ended up being the value passed to tracker_obj_simulated. This was one example of how static type checking can be helpful!