add mypy to CI

[atravitz]

PR Author Checklist

• add news item if changes are user-facing
• run pre-commit.ci autofix when the PR is ready for review

Tips

• Comment "pre-commit.ci autofix" to have pre-commit.ci auto-format your PR.
  Since this will create a commit, it is best to make this comment when you are finished with your work.

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

Reviewer Checklist

• news entry has been added if necessary
• pre-commit auto fix has been run
• any API breaks have been documented

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.24%. Comparing base (527c712) to head (49fd5a8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #178   +/-   ##
=======================================
  Coverage   92.24%   92.24%           
=======================================
  Files          84       84           
  Lines        2618     2618           
=======================================
  Hits         2415     2415           
  Misses        203      203           

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