fix(PydanticDTO): enforce explicit specification for Optional fields and ensure default factory usage for list fields

[andrewsapw]

Description

• When Pydantic model has field annotated as Optional and without default value or default factory - it still must be explicitly specified
• When Pydantic model has field annotated as list and has default factory - default factory must be used when initializing model without providing value for this field

Also, fixed test_field_definition_implicit_optional_default test, that checked if Optional field without default / default_factory converts to field with None as default value, although similar msgspec model converts it to field with Empty value

Closes

Partially closes #4232

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.38%. Comparing base (1e0dc7c) to head (8807254).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4236      +/-   ##
==========================================
- Coverage   98.38%   98.38%   -0.01%     
==========================================
  Files         348      348              
  Lines       15895    15891       -4     
  Branches     1756     1754       -2     
==========================================
- Hits        15638    15634       -4     
  Misses        121      121              
  Partials      136      136              

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[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/4236