request method
Implementation
Future<RxResult<T>> request() async {
//重要:当轮询启用时,这将返回首次的结果,底层流将被取消。
//要获得所有响应结果,你必须使用execute()或者直接监听executeStream()。
// IMPORTANT: When polling is enabled, this will return the *first* result
// and the underlying stream will be cancelled. To get all polling results,
// you must use execute() or listen to executeStream() directly.
return await executeStream().first;
}