fix: persist search page scroll offset between rebuilds (#22733)

fix: persist search scroll between rebuilds

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/lib/domain/services/timeline.service.dart

@@ -203,7 +203,7 @@ class TimelineService {
   Future<void> dispose() async {
     await _bucketSubscription?.cancel();
     _bucketSubscription = null;
-    _buffer.clear();
+    _buffer = [];
     _bufferOffset = 0;
   }
 }