Add mypy to the pre-commit hooks

[jacobtomlinson]

Now that mypy is passing we can add it to the pre-commit hooks.

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 95.33%. Comparing base (87063fc) to head (ce4648e).
Report is 119 commits behind head on main.

Files with missing lines	Patch %	Lines
kr8s/_exec.py	70.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #421      +/-   ##
==========================================
+ Coverage   94.61%   95.33%   +0.71%     
==========================================
  Files          29       31       +2     
  Lines        3141     3662     +521     
==========================================
+ Hits         2972     3491     +519     
- Misses        169      171       +2     

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