Require sqlalchemy>=2 and upgrade code.

[tobiasraabe]

Closes #439.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ac44212) 97.83% compared to head (320a096) 97.83%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #544   +/-   ##
=======================================
  Coverage   97.83%   97.83%           
=======================================
  Files         106      106           
  Lines        8976     8976           
=======================================
  Hits         8782     8782           
  Misses        194      194           

Flag	Coverage Δ
end_to_end	82.67% <100.00%> (ø)
integration	40.70% <87.50%> (ø)
unit	69.22% <93.75%> (ø)

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