fix: Trigger onChange for index on aggregation event update

lib/src/room.dart

@@ -1116,7 +1116,10 @@ class Room {
     return;
   }
 
-  /// Creates a timeline from the store. Returns a [Timeline] object.
+  /// Creates a timeline from the store. Returns a [Timeline] object. If you
+  /// just want to update the whole timeline on every change, use the [onUpdate]
+  /// callback. For updating only the parts that have changed, use the
+  /// [onChange], [onRemove] and the [onInsert] callbacks.
   Future<Timeline> getTimeline({
     void Function(int index)? onChange,
     void Function(int index)? onRemove,

lib/src/timeline.dart

@@ -245,6 +245,10 @@ class Timeline {
     _removeEventFromSet(events, event);
     // add the new one
     events.add(event);
+    if (onChange != null) {
+      final index = _findEvent(event_id: relationshipEventId);
+      onChange?.call(index);
+    }
   }
 
   void removeAggregatedEvent(Event event) {
@@ -330,6 +334,7 @@ class Timeline {
           }
 
           addAggregatedEvent(newEvent);
+
           onInsert?.call(index);
         }
       }