[python] reserve generated helper and pydantic model_* property names

[fa0311]

Property names that collide with the generated helpers or with pydantic's model_* namespace are not currently escaped, and they break the generated model in a couple of ways.

A property named from_dict (or to_dict, to_json, to_str, from_json) shadows the classmethod generated on every model:

Reserved.from_dict({...})   # AttributeError: from_dict

A property named model_config is worse — the class-level model_config = ConfigDict(...) assignment clobbers the field, so the value is silently accepted and then dropped from serialization. model_dump, model_fields, model_validate etc. shadow the pydantic methods the generated code itself calls.

These are all real-world-plausible field names (e.g. ML APIs with a model_config field), so this is a silent data loss / crash rather than a theoretical concern.

The fix treats those names as reserved words, reusing the sets the generator already maintains (GENERATED_MODEL_MEMBER_NAMES and the model_* entries of PYDANTIC_BASE_MODEL_MEMBER_NAMES). They get the usual var_ prefix and keep their wire name through the alias, exactly like schema / json / field today:

var_model_config: Optional[StrictStr] = Field(default=None, alias="model_config")

Names that merely share the prefix, like model_configuration, are untouched.

Added a unit test for the mangling, and updated testUnmappedMemberCollisionsRemainOutsideNameMappingValidation, which pinned the old (broken) unmapped output — it now expects the mangled fields. PythonClientCodegenTest passes and the python samples are unchanged.

PR checklist

• Read the contribution guidelines.
• Ran ./mvnw clean package and regenerated the python samples (no diff).
• Filed the PR against master.

/cc @cbornet @tomplus @krjakbrjak

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Summary by cubic

Reserve Python model property names that collide with generated helpers and pydantic model_* methods to prevent crashes and silent data loss. Fields like to_dict and model_config now mangle to var_* while keeping their wire names via aliases.

• Bug Fixes
  • Reserve helper names (from_dict, to_dict, to_json, to_str, from_json) and pydantic model_* methods (model_config, model_dump, model_fields, etc.).
  • Mangle to var_<name> with alias="<wire_name>"; similar names (e.g., model_configuration) are not affected.
  • Updated tests and docs; generator tests pass; Python samples unchanged.

^{Written for commit c6f1d00. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}