Revert default date-time behaviour to respect OpenAPI/JSON Schema specifications

[mueslo]

fixes #2441

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.13%. Comparing base (75f4241) to head (cafe132).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2442      +/-   ##
==========================================
- Coverage   98.13%   98.13%   -0.01%     
==========================================
  Files          66       66              
  Lines        8273     8272       -1     
  Branches      828      827       -1     
==========================================
- Hits         8119     8118       -1     
  Misses        115      115              
  Partials       39       39              

Flag	Coverage Δ
unittests	98.13% <100.00%> (-0.01%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #2442 will not alter performance

_{Comparing mueslo:patch-1 (cafe132) with main (75f4241)}

Summary

✅ 32 untouched benchmarks