Enhance OpenAPI Generator Pydantic Models with typings

[mridang]

Title: Enhance OpenAPI Generator Pydantic Models with Explicit __init__ Signatures for Snake‑case Fields

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What

Our generated Pydantic models only declare field aliases, not an explicit constructor signature, so MyPy reports errors when consuming code passes snake_case keyword arguments:

Minimal example

# Generated by OpenAPI Generator (no explicit __init__)
class V2SetHumanProfile(BaseModel):
    given_name: Annotated[str, Field(alias="givenName")]
    family_name: Annotated[str, Field(alias="familyName")]
    # … other fields …

# In test or client code:
profile = V2SetHumanProfile(
    given_name="John",
    family_name="Doe",
)

spec/sdk_test.py:35: error: Unexpected keyword argument "given_name" for "V2SetHumanProfile"; did you mean "givenName"?  [call-arg]

At runtime, Pydantic’s populate_by_name=True accepts given_name/family_name, but MyPy only “sees” the aliased fields and so flags the snake_case kwargs as invalid.

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Why

• Improved DX & autocompletion
  Developers expect Python‑style constructor arguments (given_name, not givenName).
• Stronger static guarantees
  Eliminates the need for # type: ignore[call-arg] or hand‑written stubs.
• Consistency
  Keeps runtime behavior and static types in sync.

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How

1. Inject explicit __init__ in the generator template
   Update the Jinja2 model template to emit a constructor exposing snake_case names:

2. (Alternative) Generate .pyi stubs
   Produce companion stub files with explicit __init__ signatures.

3. Regenerate the SDK & validate

   • Run the generator with the updated template.
   • Confirm constructors accept snake_case args.
   • Verify MyPy passes without ignores.