phase3: util_web + shop_scroll (custom scroll) null-safe; global Key? param fix

lib/utils/shop_scroll_controller.dart

@@ -38,7 +38,7 @@ class ShopScrollController extends ScrollController {
   final bool keepScrollOffset;
 
   /// [toString]输出中使用的标签。 旨在帮助在调试输出中标识滚动控制器实例。
-  final String debugLabel;
+  final String? debugLabel;
 
   /// The currently attached positions. 当前附加的 [positions]。
   /// 这不应直接突变。 可以使用[attach]和[detach]添加和删除[ScrollPosition]对象。
@@ -61,7 +61,7 @@ class ShopScrollController extends ScrollController {
         'ScrollController not attached to any scroll views.');
     assert(_positions.length == 1,
         'ScrollController attached to multiple scroll views.');
-    return _positions.single;
+    return _positions.single as ShopScrollPosition;
   }
 
   /// 可滚动小部件的当前滚动偏移量
@@ -83,12 +83,12 @@ class ShopScrollController extends ScrollController {
   /// 持续时间不能为零。 要在没有动画的情况下跳至特定值，请使用[jumpTo]。
   Future<void> animateTo(
     double offset, {
-    @required Duration duration,
-    @required Curve curve,
+    required Duration duration,
+    required Curve curve,
   }) {
     assert(_positions.isNotEmpty,
         'ScrollController not attached to any scroll views.');
-    final List<Future<void>> animations = List<Future<void>>(_positions.length);
+    final List<Future<void>> animations = List<Future<void>>.filled(_positions.length, Future<void>.value());
     for (int i = 0; i < _positions.length; i += 1)
       animations[i] =
           _positions[i].animateTo(offset, duration: duration, curve: curve);
@@ -149,7 +149,7 @@ class ShopScrollController extends ScrollController {
   ///     则它将是前一个实例。 当环境已更改并且[Scrollable]需要重新创建[ScrollPosition]
   ///     对象时，将使用此方法。 第一次创建[ScrollPosition]时为null。
   ScrollPosition createScrollPosition(ScrollPhysics physics,
-      ScrollContext context, ScrollPosition oldPosition) {
+      ScrollContext context, ScrollPosition? oldPosition) {
     return ShopScrollPosition(
       coordinator: coordinator,
       physics: physics,
@@ -175,7 +175,7 @@ class ShopScrollController extends ScrollController {
   @mustCallSuper
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
-    if (debugLabel != null) description.add(debugLabel);
+    if (debugLabel != null) description.add(debugLabel!);
     if (initialScrollOffset != 0.0)
       description.add(
           'initialScrollOffset: ${initialScrollOffset.toStringAsFixed(1)}, ');