* fix: handle const keyword in google genai tool schemas
* fix: handle pydantic ValidationError in Google GenAI client
Fixes Datadog error tracking issue where pydantic_core.ValidationError
was raised when tool schemas contained unsupported fields (e.g., 'const',
'default', 'additionalProperties').
Changes:
- Add error handling for pydantic ValidationError in request(), request_async(), and stream_async()
- Convert validation errors to LLMBadRequestError with helpful error message
- Deep copy tool parameters before cleaning to avoid modifying shared objects
- Add imports for pydantic_core and copy module
This prevents unhandled exceptions and provides better diagnostics when
tool schemas contain fields not supported by Google AI API.