[Feature Request]: Structured Outputs with Pydantic

[alckasoc]

Feature Description

Instead of a list of dictionaries (Python native types), we can organize the outputs into Pydantic objects to organize data and attach metadata. Will be useful later.

ATTENTION: Only include the structured outputs for the refactored agents (ReAct, Self-Refine, and CRITIC) for now.

Reason

Here's an example:

class ReflexionCoTOutput(BaseModel):
    """The output of the ReflexionCoT agent.
    Attributes:
        is_correct (bool): Whether the answer is correct.
        answer (str): The generated answer.
        thought (str): The thought generated by the agent.
        action (str): The action taken by the agent.
        observation (str): The observation made by the agent.
    """

    is_correct: bool = Field(..., description="Whether the answer is correct.")
    answer: str = Field(..., description="The generated answer.")
    thought: str = Field(..., description="The thought generated by the agent.")
    action: str = Field(..., description="The action taken by the agent.")
    observation: str = Field(..., description="The observation made by the agent.")

Additionally, for each agent, for all strategies, the list of dictionaries should have the same keys. For each agent, the agent should have a single Pydantic class that structures all the outputs.