add client function for debugging movement data

src/FunctionCompiler.cc

@@ -313,6 +313,8 @@ static vector<shared_ptr<CompiledFunctionCode>> compile_function_code(
           compiled->description = it.second;
         } else if (it.first == "client_flag") {
           compiled->client_flag = stoull(it.second, nullptr, 0);
+        } else if (it.first == "show_return_value") {
+          compiled->show_return_value = true;
         } else {
           throw runtime_error("unknown metadata key: " + it.first);
         }