refactor(mobile): Use widgets in Immich asset grid (#7140)

* Refactors to use widgets in immich asset grid

Adds comments

* Fixes asset thumbnail absoluteOffset

* feat(mobile): Uses gradient image placeholders in memory lane and in the asset grid (#7142)

* Uses gradient image placeholders in memory lane and in the asset grid

* Changes to create placeholders in immmich image.thumbnail

* removed unused import

* uses context.isDarkTheme and fixed function signature for allAssetsSelected

mobile/lib/modules/memories/ui/memory_lane.dart

@@ -2,6 +2,7 @@ import 'package:auto_route/auto_route.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:immich_mobile/modules/home/ui/asset_grid/thumbnail_placeholder.dart';
 import 'package:immich_mobile/modules/memories/providers/memory.provider.dart';
 import 'package:immich_mobile/routing/router.dart';
 import 'package:immich_mobile/shared/ui/immich_image.dart';
@@ -60,7 +61,10 @@ class MemoryLane extends HookConsumerWidget {
                                     fit: BoxFit.cover,
                                     width: 130,
                                     height: 200,
-                                    useGrayBoxPlaceholder: true,
+                                    placeholder: const ThumbnailPlaceholder(
+                                      width: 130,
+                                      height: 200,
+                                    ),
                                   ),
                                 ),
                               ),