Paging on iOS: a shared paged-list presenter #370

Part of #356 (Phase 2).

Why

MarketListViewModel.pagedMarketList is a Flow<PagingData<MarketModel>>. Android consumes it with collectAsLazyPagingItems(); SwiftUI has no equivalent.

Scope

• In a shared module, a small PagedListPresenter<T> built on Paging common's PagingDataPresenter. It exposes:
  • items: StateFlow<List<T>>
  • loadState: StateFlow<CombinedLoadStates>
  • fun get(index: Int), which triggers the next page the way LazyPagingItems[index] does
  • refresh() and retry()
• SwiftUI's List calls get(index) from onAppear of each row, and .refreshable calls refresh().
• Android keeps collectAsLazyPagingItems() and doesn't use the presenter.
• commonTest for the presenter, using TestPager/a fake PagingSource.