feat: support initial state when creating session in short term memory

[mrcaidev]

ShortTermMemory 的 create_session 接口支持传入可选的 state 参数，直接透传给底层的 session_service。

该参数可以用于在创建会话时，就注入会话状态。例如，在创建会话之前，创建一个沙箱，并将其元数据绑定到会话状态中。

[Copilot]

Pull request overview

为 ShortTermMemory.create_session 增加可选的初始 state 参数，用于在创建会话时将状态透传到底层 session_service，以支持在会话创建阶段注入会话元数据/上下文。

Changes:

• 为 ShortTermMemory.create_session 新增 state: dict | None = None 参数
• 更新 create_session docstring，补充 state 参数说明
• 创建新 session 时将 state 透传给底层 session_service.create_session(...)

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[Copilot]

Pull request overview

This PR extends ShortTermMemory.create_session() to accept an optional initial state and forwards it to the underlying ADK session_service, enabling callers to inject session metadata at session-creation time (e.g., sandbox metadata binding).

Changes:

• Add optional state parameter to ShortTermMemory.create_session(...).
• Update docstring to clarify state semantics (applied only on new session creation; ignored if the session already exists).
• Forward state to the underlying BaseSessionService.create_session(...) call.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.