Add regex_engine="python-re" if regex uses lookaround

[camillol]

Pydantic 2 uses Rust's regex implementation by default, which runs in linear time but doesn't support lookarounds or backreferences. If a field needs to use such a regex, it is necessary to set up the model's config to use Python's regex engine instead. See documentation.

This change adds the necessary config when generating Pydantic 2 models that contain a field with a pattern containing lookarounds.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

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  Hits            ?     4125           
  Misses          ?       47           
  Partials        ?       17           

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unittests	98.13% <100.00%> (?)

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[codspeed-hq]

CodSpeed Performance Report

Merging #1945 will not alter performance

_{Comparing camillol:regex_engine (cdcd01d) with main (fcab9a4)}

Summary

✅ 29 untouched benchmarks