endpoint.close()
正常关闭端点。当所有当前打开的会话关闭时，端点将关闭并销毁自身。一旦调用，新会话将被拒绝。
¥Gracefully close the endpoint. The endpoint will close and destroy itself when all currently open sessions close. Once called, new sessions will be rejected.
返回一个在端点被销毁时实现的 promise。
¥Returns a promise that is fulfilled when the endpoint is destroyed.