fix(mobile): mobile album sort not persisting (#5584)

* chore(deps): use mocktail instead of mockito

* refactor: move stubs to fixtures/

* fix: fetch assetsortmode based on storeindex

* test: validate AlbumSortByOptions provider

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>

mobile/test/fixtures/asset.stub.dart

@@ -0,0 +1,37 @@
+import 'package:immich_mobile/shared/models/asset.dart';
+
+final class AssetStub {
+  const AssetStub._();
+
+  static final image1 = Asset(
+    checksum: "image1-checksum",
+    localId: "image1",
+    ownerId: 1,
+    fileCreatedAt: DateTime.now(),
+    fileModifiedAt: DateTime.now(),
+    updatedAt: DateTime.now(),
+    durationInSeconds: 0,
+    type: AssetType.image,
+    fileName: "image1.jpg",
+    isFavorite: true,
+    isArchived: false,
+    isTrashed: false,
+    stackCount: 0,
+  );
+
+  static final image2 = Asset(
+    checksum: "image2-checksum",
+    localId: "image2",
+    ownerId: 1,
+    fileCreatedAt: DateTime(2000),
+    fileModifiedAt: DateTime(2010),
+    updatedAt: DateTime.now(),
+    durationInSeconds: 60,
+    type: AssetType.video,
+    fileName: "image2.jpg",
+    isFavorite: false,
+    isArchived: false,
+    isTrashed: false,
+    stackCount: 0,
+  );
+}