refactor chatview to have two sliver lists

Co-authored-by: Erwan Leboucher <erwanleboucher@gmail.com>

lib/controllers/room_chat.dart

@@ -29,16 +29,9 @@ class RoomChatController(final String roomId)
 
     if (!room.hasFetchedState) {
       final state = await client.getRoomState(.new(roomId: roomId));
-
       await ref.read(RoomsController.provider.notifier).addState(roomId, state);
     }
 
-    // While there are under 20 events, try to load more
-    // until there's no more or the conditions are met.
-    if (room.hasMore && room.timeline.length < 20) {
-      loadOlder();
-    }
-
     return room.timeline
         .toEntryIList(compare: (a, b) => (a?.key ?? 0).compareTo(b?.key ?? 0))
         .map((element) => element.value)