session.close()
启动会话的正常关闭。允许现有流完成，但不会打开任何新流。一旦所有流都关闭，会话将被销毁。会话被销毁后，返回的 promise 将被实现。
¥Initiate a graceful close of the session. Existing streams will be allowed to complete but no new streams will be opened. Once all streams have closed, the session will be destroyed. The returned promise will be fulfilled once the session has been destroyed.