Add explicit using System.IO for IOException

Co-authored-by: SteveSandersonMS <1101362+SteveSandersonMS@users.noreply.github.com>

Author: Copilot

dotnet/src/Types.cs

@@ -2,6 +2,7 @@
  *  Copyright (c) Microsoft Corporation. All rights reserved.
  *--------------------------------------------------------------------------------------------*/
 
+using System.IO;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using Microsoft.Extensions.AI;