Fix compilation error

Author: alex-kulakov

Orm/Xtensive.Orm.Tests.Framework/Cloner.cs

@@ -1,9 +1,11 @@
-// Copyright (C) 2003-2010 Xtensive LLC.
-// All rights reserved.
-// For conditions of distribution and use, see license.
+// Copyright (C) 2009-2025 Xtensive LLC.
+// This code is distributed under MIT license terms.
+// See the License.txt file in the project root for more information.
 // Created by: Alex Yakunin
 // Created:    2009.05.05
 
+using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Runtime.Serialization;
 using System.Runtime.Serialization.Formatters.Binary;