Fix VM memory allocation optimizations by reducing what we allocate on the heap

internal/builtins/lower.go

@@ -16,6 +16,6 @@ func Lower(args ...object.Object) object.Object {
 		return newError(err.Error())
 	}
 
-	str := args[0].(*object.String)
-	return &object.String{Value: strings.ToLower(str.Value)}
+	str := args[0].(object.String)
+	return object.String{Value: strings.ToLower(str.Value)}
 }