Added three sizes of book cover small medium and large to be returned as cover_url.

src/Api/AbstractBookInfo.php

@@ -10,7 +10,7 @@ abstract class AbstractBookInfo
     public string $description;
     public string $title;
     public string $category;
-    public string $cover_url;
+    public array $cover_url;
     public int $pages;
     public string $cycle;
     public int $volume;