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

internal/builtins/readfile.go

@@ -16,11 +16,11 @@ func ReadFile(args ...object.Object) object.Object {
 		return newError(err.Error())
 	}
 
-	filename := args[0].(*object.String).Value
+	filename := args[0].(object.String).Value
 	data, err := os.ReadFile(filename)
 	if err != nil {
 		return newError("IOError: error reading from file %s: %s", filename, err)
 	}
 
-	return &object.String{Value: string(data)}
+	return object.String{Value: string(data)}
 }