refactor(mobile): repositories for album service (#12701)

* refactor(mobile): repositories for album service

* review feedback, first service unit test

mobile/lib/repositories/backup.repository.dart

@@ -0,0 +1,20 @@
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:immich_mobile/entities/backup_album.entity.dart';
+import 'package:immich_mobile/interfaces/backup.interface.dart';
+import 'package:immich_mobile/providers/db.provider.dart';
+import 'package:isar/isar.dart';
+
+final backupRepositoryProvider =
+    Provider((ref) => BackupRepository(ref.watch(dbProvider)));
+
+class BackupRepository implements IBackupRepository {
+  final Isar _db;
+
+  BackupRepository(
+    this._db,
+  );
+
+  @override
+  Future<List<String>> getIdsBySelection(BackupSelection backup) =>
+      _db.backupAlbums.filter().selectionEqualTo(backup).idProperty().findAll();
+}