fix json-or-python serializer as JSON object key

[davidhewitt]

Change Summary

Change json-or-python serializer to delegate to the json serializer to decide what to do as a JSON key.

Related issue number

Fixes pydantic/pydantic#6795

Checklist

• Unit tests for the changes exist
• Documentation reflects the changes where applicable
• Pydantic tests pass with this pydantic-core (except for expected changes)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[codecov]

Codecov Report

Merging #903 (843a8b4) into main (a4015ab) will increase coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #903      +/-   ##
==========================================
+ Coverage   93.74%   93.78%   +0.03%     
==========================================
  Files         105      105              
  Lines       15331    15331              
  Branches       25       25              
==========================================
+ Hits        14372    14378       +6     
+ Misses        953      947       -6     
  Partials        6        6              

Files Changed	Coverage Δ
src/serializers/type_serializers/json_or_python.rs	97.95% <100.00%> (+12.24%)	⬆️

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[codspeed-hq]

CodSpeed Performance Report

Merging #903 will degrade performances by 13.9%

_{Comparing dh/json-or-python-key-ser (843a8b4) with main (a4015ab)}

Summary

❌ 1 regressions
✅ 137 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	dh/json-or-python-key-ser	Change
❌	test_model_exclude_unset_false	63.7 µs	74 µs	-13.9%