Fix memory leaks in CupertinoSwitch (#147821)

Author: ValentinVignal

packages/flutter/lib/src/cupertino/switch.dart

@@ -200,10 +200,10 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
   late HorizontalDragGestureRecognizer _drag;
 
   late AnimationController _positionController;
-  late CurvedAnimation position;
+  late final CurvedAnimation position;
 
   late AnimationController _reactionController;
-  late Animation<double> _reaction;
+  late CurvedAnimation _reaction;
 
   late bool isFocused;
 
@@ -424,6 +424,8 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
 
     _positionController.dispose();
     _reactionController.dispose();
+    position.dispose();
+    _reaction.dispose();
     super.dispose();
   }
 }

packages/flutter/test/cupertino/switch_test.dart

@@ -14,9 +14,13 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
 
 void main() {
-  testWidgets('Switch can toggle on tap', (WidgetTester tester) async {
+  testWidgets('Switch can toggle on tap',
+    // TODO(polina-c): remove when fixed https://github.com/flutter/flutter/issues/145600 [leak-tracking-opt-in]
+    experimentalLeakTesting: LeakTesting.settings.withTracked(classes: const <String>['CurvedAnimation']),
+    (WidgetTester tester) async {
     final Key switchKey = UniqueKey();
     bool value = false;
     await tester.pumpWidget(