Use mypy via pre-commit instead of pytest-mypy

[dionhaefner]

This should prevent the never ending issue with tests breaking because of mypy updates.

[codecov]

Codecov Report

Merging #319 (98c3e3a) into main (71f2c2a) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 66.66%.

@@           Coverage Diff            @@
##             main     #319    +/-   ##
========================================
  Coverage   98.11%   98.11%            
========================================
  Files          52       52            
  Lines        2335     2338     +3     
  Branches      327      476   +149     
========================================
+ Hits         2291     2294     +3     
  Misses         29       29            
  Partials       15       15            

Files	Coverage Δ
terracotta/drivers/sqlite_remote_meta_store.py	100.00% <100.00%> (ø)
terracotta/server/flask_api.py	96.20% <0.00%> (ø)
terracotta/scripts/migrate.py	73.21% <66.66%> (+0.99%)	⬆️

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