genai: Fix required field is ignored when dealing with nested pydantic models

[ghengao]

PR Description

Fix missing required field in the tool schema when dealing with nested pydantic models. Following model

class MyModel(BaseModel):
    name: str
    age: int

class Models(BaseModel):
    models: list[MyModel]

Is not populating required field for nested MyModel

"function_declarations": [
            {
                "description": "",
                "name": "Models",
                         ...
                        "models": {
                            "description": "",
                            "enum": [],
                            "format_": "",
                            "items": {
                                "description": "MyModel",
                                "enum": [],
                            ...
                                    },
                                },
                                "required": [],   # <- Should be "required": ["name", "age"],
                                "type_": 6,
                            },
                            ...
                        }
                    },
                    "required": ["models"],
                    "type_": 6,
                },
            }
        ]
    }

Relevant issues

Fixes #690,

Type

🐛 Bug Fix

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