Remove flutter chat (#26)

Had to squash merge manually as Forgejo was erroring

lib/controllers/reactions_controller.dart

@@ -0,0 +1,56 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/controllers/client_controller.dart";
+import "package:nexus/controllers/rooms_controller.dart";
+import "package:nexus/models/configs/reactions_config.dart";
+import "package:nexus/models/content/reaction.dart";
+import "package:nexus/models/requests/get_related_events_request.dart";
+
+class ReactionsController extends AsyncNotifier<IMap<String, IList<String>>> {
+  final ReactionsConfig config;
+  ReactionsController(this.config);
+
+  @override
+  Future<IMap<String, IList<String>>> build() async {
+    final eventInfo = ref.watch(
+      RoomsController.provider.select((value) {
+        final event = value[config.roomId]?.events[config.eventRowId];
+        return event == null ? null : (event.eventId, event.reactions);
+      }),
+    );
+
+    final reactionEvents = eventInfo?.$2.isNotEmpty == true
+        ? await ref
+              .watch(ClientController.provider.notifier)
+              .getRelatedEvents(
+                GetRelatedEventsRequest(
+                  roomId: config.roomId,
+                  eventId: eventInfo!.$1,
+                  relationType: "m.annotation",
+                ),
+              )
+        : null;
+
+    return reactionEvents
+            ?.where((event) => event.redactedBy == null)
+            .fold<IMap<String, IList<String>>>(IMap(), (acc, event) {
+              if (event.content case ReactionContent(:final key?)) {
+                return acc.update(
+                  key,
+                  (list) => list.add(event.sender),
+                  ifAbsent: () => IList([event.sender]),
+                );
+              }
+
+              return acc;
+            }) ??
+        const IMap.empty();
+  }
+
+  static final provider =
+      AsyncNotifierProvider.family<
+        ReactionsController,
+        IMap<String, IList<String>>,
+        ReactionsConfig
+      >(ReactionsController.new);
+}