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 certain rules which we should address over time.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.61%. Comparing base (8731ef9) to head (9872485).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1731   +/-   ##
=======================================
  Coverage   99.61%   99.61%           
=======================================
  Files          23       23           
  Lines        5917     5917           
=======================================
  Hits         5894     5894           
  Misses         23       23           

Flag	Coverage Δ
unittests	99.61% <ø> (ø)

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