public RowAsyncEnumerator(
            BigtableClientImpl client,
            ReadRowsRequest originalRequest,
            CallSettings callSettings,
            RetrySettings retrySettings)
        {
            _client        = client;
            _callSettings  = callSettings;
            _retrySettings = retrySettings;

            _requestManager = new BigtableReadRowsRequestManager(originalRequest);
        }
        public RowAsyncEnumerator(
            BigtableClientImpl client,
            ReadRowsRequest originalRequest,
            CallSettings callSettings,
            RetrySettings retrySettings,
            BigtableServiceApiClient.ReadRowsStream stream)
        {
            _client        = client;
            _callSettings  = callSettings;
            _retrySettings = retrySettings;
            _stream        = stream;

            _requestManager = new BigtableReadRowsRequestManager(originalRequest);
        }