fix(function_schema): raise UserError for Pydantic protected-namespace param names

[devteamaegis]

What's broken

Calling function_schema() (or @function_tool) on a function whose parameter is named model_dump, model_dump_json, model_validate, model_validate_json, or model_validate_strings raises an unhandled ValueError deep inside Pydantic's create_model(). The traceback points into Pydantic internals and gives no hint that the parameter name is the problem or how to fix it.

Why it happens

Pydantic treats field names that match built-in BaseModel methods as belonging to a protected namespace and raises ValueError inside create_model(). These five names are distinct from model_config / model_fields / model_computed_fields covered by PR #3548.

Fix

A guard clause before create_model() in function_schema.py detects any field name in the protected set and raises a UserError with an actionable message listing the offending parameter names, before Pydantic ever sees them.

Test

Added test_pydantic_protected_namespace_param_raises_user_error in test_function_schema.py, which asserts that a function with a model_validate parameter raises UserError (not ValueError) and that the error message names the conflicting parameter.

Fixes #3549