Fix #17754: Convert OpenAPI types to Python types in anyOf/oneOf

[pgoslatara]

• Add toPythonType() helper method to convert OpenAPI types (string, array) to Python types (str, List)
• Override postProcessModels() to convert anyOf/oneOf types in AbstractPythonCodegen and AbstractPythonPydanticV1Codegen
• Add test case to verify anyOf with string and array types generates correct Python types

Before: anyOf schemas contained ['array[string]', 'string']
After: anyOf schemas contain ['List[str]', 'str']

Fixes #17754.

Python technical committee: @cbornet @tomplus @krjakbrjak @fa0311 @multani

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Summary by cubic

Fixes #17754 by converting anyOf/oneOf OpenAPI types to proper Python types in generated Python clients. Schemas like array[string] now render as List[str], and string as str.

• Bug Fixes
  • Added toPythonType helper to map OpenAPI types (string, array, map, etc.) to Python types (str, List, Dict, etc.).
  • Post-processed models in AbstractPythonCodegen and AbstractPythonPydanticV1Codegen to convert anyOf/oneOf entries.
  • Added a test and sample spec to verify anyOf contains ["List[str]", "str"] instead of ["array[string]", "string"].

^{Written for commit c357866. Summary will update on new commits.}