feat: add undo

app/src/main/java/chess/controller/commands/CastlingCommand.java

@@ -16,7 +16,7 @@ public class CastlingCommand extends PlayerCommand {
 	}
 
 	@Override
-	public void undo(Game game, OutputSystem outputSystem) {
+	public CommandResult undo(Game game, OutputSystem outputSystem) {
 		// TODO Auto-generated method stub
 		throw new UnsupportedOperationException("Unimplemented method 'undo'");
 	}