Itunes Remote implementation.

ItunesRemote.swift

// 1
final class ItunesRemote: ObservableObject {

  // 2
    struct ItunesCategorySection: IdentifiableHashable {
        let sectionID: ItunesCategoryIdentifier
        let cellIDs: [FeedItemViewModel]
        var id: ItunesCategoryIdentifier { sectionID }
    }

  // 3
    private let service = ItunesClient()
  // 4
    private var cancellables: Set<AnyCancellable> = []
    @Published var itunesSections: [ItunesSection] = []
}