fix: replace deprecated withOpacity with withValues

Author: LinXunFeng

example/lib/features/listview/listview_dynamic_offset/listview_dynamic_offset_page.dart

@@ -81,7 +81,7 @@ class _ListViewDynamicOffsetPageState extends State<ListViewDynamicOffsetPage> {
             },
           ),
           Container(
-            color: Colors.grey.withOpacity(_navBgAlpha),
+            color: Colors.grey.withValues(alpha: _navBgAlpha),
             child: Column(
               mainAxisSize: MainAxisSize.min,
               children: [
@@ -158,8 +158,8 @@ class _ListViewDynamicOffsetPageState extends State<ListViewDynamicOffsetPage> {
                 style: TextStyle(
                   fontSize: 17,
                   fontWeight: FontWeight.bold,
-                  color: Colors.black54.withOpacity(
-                    _isShowNavTitle ? 1 : 0,
+                  color: Colors.black54.withValues(
+                    alpha: _isShowNavTitle ? 1 : 0,
                   ),
                 ),
               ),

example/lib/features/pageview/pageview_demo/pageview_parallax_item_listener_page.dart

@@ -231,7 +231,7 @@ class _ParallaxItemViewState extends State<ParallaxItemView> {
       width: 80,
       height: 80,
       decoration: BoxDecoration(
-        color: Colors.white.withOpacity(0.8),
+        color: Colors.white.withValues(alpha: 0.8),
         borderRadius: BorderRadius.circular(10),
       ),
       child: Text("Page $index"),

example/lib/features/pageview/pageview_demo/pageview_parallax_page.dart

@@ -175,7 +175,7 @@ class _PageViewParallaxPageState extends State<PageViewParallaxPage> {
       width: 80,
       height: 80,
       decoration: BoxDecoration(
-        color: Colors.white.withOpacity(0.8),
+        color: Colors.white.withValues(alpha: 0.8),
         borderRadius: BorderRadius.circular(10),
       ),
       child: Text("Page $index"),