Fix memory leaks in CupertinoTextMagnifier (#147208)

Author: ValentinVignal

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

@@ -82,8 +82,10 @@ class _CupertinoTextMagnifierState extends State<CupertinoTextMagnifier>
   // set these values.
   Offset _currentAdjustedMagnifierPosition = Offset.zero;
   double _verticalFocalPointAdjustment = 0;
-  late AnimationController _ioAnimationController;
-  late Animation<double> _ioAnimation;
+  late final AnimationController _ioAnimationController;
+  late final Animation<double> _ioAnimation;
+  late final CurvedAnimation _ioCurvedAnimation;
+
 
   @override
   void initState() {
@@ -97,20 +99,21 @@ class _CupertinoTextMagnifierState extends State<CupertinoTextMagnifier>
     widget.controller.animationController = _ioAnimationController;
     widget.magnifierInfo
         .addListener(_determineMagnifierPositionAndFocalPoint);
-
+    _ioCurvedAnimation = CurvedAnimation(
+      parent: _ioAnimationController,
+      curve: widget.animationCurve,
+    );
     _ioAnimation = Tween<double>(
       begin: 0.0,
       end: 1.0,
-    ).animate(CurvedAnimation(
-      parent: _ioAnimationController,
-      curve: widget.animationCurve,
-    ));
+    ).animate(_ioCurvedAnimation);
   }
 
   @override
   void dispose() {
     widget.controller.animationController = null;
     _ioAnimationController.dispose();
+    _ioCurvedAnimation.dispose();
     widget.magnifierInfo
         .removeListener(_determineMagnifierPositionAndFocalPoint);
     super.dispose();

packages/flutter/test/material/selection_area_test.dart

@@ -9,6 +9,7 @@ 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';
 
 import '../widgets/process_text_utils.dart';
 
@@ -288,7 +289,10 @@ void main() {
     expect(content!.plainText, 'How');
   });
 
-  testWidgets('stopping drag of end handle will show the toolbar', (WidgetTester tester) async {
+  testWidgets('stopping drag of end handle will show the toolbar',
+    // 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 FocusNode focusNode = FocusNode();
     addTearDown(focusNode.dispose);