Migrate from mypy to ty as a type checker

[tleonhardt]

Migrate from mypy to ty for Python type checking since ty is much faster.

ty is a bit stricter out-of-the-box. The top-level ty.toml file has some configuration to ignore one type of rule check where it attempts to validate that an attribute must exist given the type.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (8731ef9) to head (4de029f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1731      +/-   ##
==========================================
- Coverage   99.61%   99.59%   -0.02%     
==========================================
  Files          23       23              
  Lines        5917     5920       +3     
==========================================
+ Hits         5894     5896       +2     
- Misses         23       24       +1     

Flag	Coverage Δ
unittests	99.59% <100.00%> (-0.02%)	⬇️

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