private void buildScalarRsp(ParseResult parseResult, ExprQueryRsp response) {
        ScalarRspData scalarRspData = new ScalarRspData();
        response.setData(scalarRspData);
        scalarRspData.setResultType(ResultType.SCALAR);
        ScalarResult scalarResult = (ScalarResult) parseResult;
        response.setStatus(ResultStatus.SUCCESS);
        //need return int type
        scalarRspData.setResult(
            new TimeValuePair(
                System.currentTimeMillis() / 1000,
                formatDoubleValue(scalarResult.getValue())
            ));
    }
OAP adopt time step by start/end,
reserve step/timeout param to keep consistent with API protocol.
oap-server/server-query-plugin/promql-plugin/src/main/java/org/apache/skywalking/oap/query/promql/handler/PromQLApiHandler.java