[Feature] AGENT_MODEL_STREAMING 阶段无法区分模型的"思考过程"和"最终答案"

### Feature Request 在 Spring AI Alibaba 1.1.2.2 的 ReactAgent 中，AGENT_MODEL_STREAMING 阶段无法区分模型的"思考过程"和"最终答案"。能否在在 Message 的 metadata 中增加 isReasoning 标记 ### Is your feature request related to a problem? Please describe _No response_ ### Describe the solution you'd like _No response_ ### Describe alternatives you've considered _No response_ ### Additional context _No response_