refactor: use riverpod's update api

packages/app/lib/src/features/home/application/feed_service.dart

@@ -37,20 +37,19 @@ base class FeedService extends _$FeedService {
     );
   }
 
+  // TODO(MattsAttack): This is just an unused example. It should be used or removed.
   /// Replace the current posts with newly generated posts.
-  Future<void> replacePosts(List<PostEntity> newPosts) async {
+  Future<FeedModel> addPosts(List<PostEntity> newPosts) async {
     // You can only change a Notifier's `state` by adding methods that assign a new value.
     // You can't mutate the state directly, nor can you change it outside of a method.
-    if (state case AsyncData<FeedModel>(:final value)) {
-      state = AsyncData(
-        value.copyWith(
-          posts: [
-            // Spread the new list into the generated list.
-            ...value.posts,
-            ...newPosts,
-          ],
-        ),
+    return await update((value) {
+      return value.copyWith(
+        posts: [
+          // Spread the new list into the generated list.
+          ...value.posts,
+          ...newPosts,
+        ],
       );
-    }
+    });
   }
 }