Always convert str subclasses to str

[adriangb]

Closes #786

Selected Reviewer: @dmontagu

[adriangb]

please review

[codecov]

Codecov Report

Merging #788 (9a68989) into main (33fea1e) will decrease coverage by 0.15%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #788      +/-   ##
==========================================
- Coverage   93.67%   93.53%   -0.15%     
==========================================
  Files          99      100       +1     
  Lines       14322    14378      +56     
  Branches       25       25              
==========================================
+ Hits        13416    13448      +32     
- Misses        900      924      +24     
  Partials        6        6              

Impacted Files	Coverage Δ
src/input/input_python.rs	98.11% <100.00%> (+0.01%)	⬆️

... and 68 files with indirect coverage changes

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[codspeed-hq]

CodSpeed Performance Report

Merging #788 will not alter performance

_{Comparing str-lax (9a68989) with main (33fea1e)}

Summary

✅ 126 untouched benchmarks

[adriangb]

Pydantic test failures are expected, we're changing the behavior