feat(ui): Cache tracked cover images for offline use

lib/src/ui/pages/anime_list.dart

@@ -101,7 +101,7 @@ class AnimeListPage extends StatelessWidget {
           body: PageView(
             // Prevent swiping between pages
             // (https://github.com/flutter/flutter/issues/37510#issuecomment-612663656)
-            physics: NeverScrollableScrollPhysics(),
+            physics: const NeverScrollableScrollPhysics(),
             controller: _controller,
             children: [
               ListView.builder(

lib/src/ui/pages/anime_search.dart

@@ -72,6 +72,7 @@ class AnimeSearchPage extends StatelessWidget {
                         child: ListItem(
                           title: item.title,
                           thumbnailUrl: item.thumbnailUrl,
+                          cached: false,
                           extra: [
                             Align(
                               alignment: Alignment.centerLeft,

lib/src/ui/widgets/image.dart

@@ -1,14 +1,19 @@
+import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/material.dart';
 
 class AnimeCoverImage extends StatelessWidget {
   const AnimeCoverImage({
     required this.url,
+    this.cached = true,
     super.key,
   });
 
   /// The URL to the cover image.
   final String url;
 
+  /// Flag indicating if the image should be cached
+  final bool cached;
+  
   @override
   Widget build(BuildContext context) {
     return ClipRRect(
@@ -19,7 +24,9 @@ class AnimeCoverImage extends StatelessWidget {
         child: DecoratedBox(
           decoration: BoxDecoration(
             image: DecorationImage(
-              image: NetworkImage(url),
+              image: cached ?
+                CachedNetworkImageProvider(url) as ImageProvider :
+                NetworkImage(url),
               fit: BoxFit.cover,
             ),
           ),

lib/src/ui/widgets/list_item.dart

@@ -10,6 +10,7 @@ class ListItem extends StatelessWidget {
     required this.title,
     this.onLeftSwipe,
     this.onRightSwipe,
+    this.cached = true,
     this.extra = const [],
     super.key,
   });
@@ -27,6 +28,9 @@ class ListItem extends StatelessWidget {
   final void Function()? onLeftSwipe;
   final void Function()? onRightSwipe;
 
+  /// Flag indicating whether the thumbnail image should be cached
+  final bool cached;
+  
   @override
   Widget build(BuildContext context) {
     return SwipeableTile.swipeToTrigger(
@@ -68,6 +72,7 @@ class ListItem extends StatelessWidget {
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
             AnimeCoverImage(
+              cached: cached,
               url: thumbnailUrl,
             ),