next method
Returns a future that completes when the next page of data is available.
Implementation
Future<PaginationState<ReturnType>> next() async {
final internalState = await _waitForInternalState();
final extractedData = internalState.extractedData;
final numBefore = internalState.numBefore;
_firstElement =
extractedData.elementAtOrNull(numBefore + _options.pageSize);
_internalStateObserver.next(null);
_doNewQuery(extractedData.elementAtOrNull(numBefore), reverseOrder: false);
return waitForData();
}