Windows PathNotFoundException fix

- Fixed the PathNotFoundException for Windows, which doesn't use "/" in directories, but "\".
(flutter: PathNotFoundException: Creation failed, path = 'C:\Users\User\AppData\Local\Temp\Mangayomi/cacheimagecover' (OS Error: Das System kann den angegebenen Pfad nicht finden.)
Instead of manually concatenating paths using string interpolation, it now uses the join function properly.
- Also fixed that the App was not able to create the directories by including recursive: true in the else statement.

lib/modules/widgets/custom_extended_image_provider.dart

@@ -192,7 +192,8 @@ class CustomExtendedNetworkImageProvider
   ) async {
     final Directory cacheImagesDirectory = Directory(join(
         (await getTemporaryDirectory()).path,
-        'Mangayomi/${imageCacheFolderName ?? "cacheimagecover"}'));
+        'Mangayomi',
+        imageCacheFolderName ?? 'cacheimagecover'));
     Uint8List? data;
     // exist, try to find cache image file
     if (cacheImagesDirectory.existsSync()) {
@@ -213,7 +214,7 @@ class CustomExtendedNetworkImageProvider
     }
     // create folder
     else {
-      await cacheImagesDirectory.create();
+      await cacheImagesDirectory.create(recursive: true);
     }
     // load from network
     if (data == null) {