fetchNextPage method
Load the next cursor page and retain normalized ID membership.
Implementation
Future<void> fetchNextPage() async {
final graph = ref.read(entityGraphProvider);
final list = graph.listState(queryKey);
if (!list.hasNextPage || list.nextCursor == null) return;
await _runWithRetry(() => _doFetch(graph, cursor: list.nextCursor));
if (!_disposed) state = AsyncValue.data(_buildSnapshot(graph));
}