refactor(mobile): services and providers (#9232)

* refactor(mobile): services and provider

* providers

mobile/lib/providers/activity_statistics.provider.dart

@@ -0,0 +1,24 @@
+import 'package:immich_mobile/providers/activity_service.provider.dart';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+
+part 'activity_statistics.provider.g.dart';
+
+/// Maintains the current number of comments by <shared-album, asset>
+@riverpod
+class ActivityStatistics extends _$ActivityStatistics {
+  @override
+  int build(String albumId, [String? assetId]) {
+    ref
+        .watch(activityServiceProvider)
+        .getStatistics(albumId, assetId: assetId)
+        .then((comments) => state = comments);
+    return 0;
+  }
+
+  void addActivity() => state = state + 1;
+
+  void removeActivity() => state = state - 1;
+}
+
+/// Mock class for testing
+abstract class ActivityStatisticsInternal extends _$ActivityStatistics {}