langchain/callbacks/manager.py/AsyncRunManager/on_text
class AsyncRunManager:    async def on_text(
        self,
        text: str,
        **kwargs: Any,
    ) -> Any:
        """Run when text is received."""
        await _ahandle_event(
            self.handlers,
            "on_text",
            None,
            text,
            run_id=self.run_id,
            parent_run_id=self.parent_run_id,
            **kwargs,
        )