Add missing methods

"Warning
 As of PHP 8.1.0, a class which implements Serializable without also implementing __serialize() and __unserialize() will generate a deprecation warning."
 https://www.php.net/manual/en/class.serializable.php

src/Mvc/Collection.php

@@ -1516,4 +1516,14 @@ public function jsonSerialize(): array
 
         return $data;
     }
+
+    public function __serialize(): array
+    {
+        return $this->toArray();
+    }
+
+    public function __unserialize(array $data): void
+    {
+        $this->assign($data);
+    }
 }