[ISSUE #1112] feat: optimize producer send async

[twz915]

What is the purpose of the change

#1112 optimize producer send async, without block (connect and sendRequest)

Comparison of the time spent sending messages

old version

new version

Example to Test

package main

import (
	"context"
	"fmt"
	"time"

	"github.com/apache/rocketmq-client-go/v2"
	"github.com/apache/rocketmq-client-go/v2/primitive"
	"github.com/apache/rocketmq-client-go/v2/producer"
)

var defaultProducer = getProducer()

func getProducer() rocketmq.Producer {
	p, err := rocketmq.NewProducer(
		producer.WithSendMsgTimeout(time.Second*3),
		producer.WithRetry(2),
	)
	if err != nil {
		panic(err)
	}
	err = p.Start()
	if err != nil {
		panic(err)
	}
	return p
}

func sendMsg(topic string, body []byte) error {
	msg := primitive.NewMessage(topic, body)
	ctx := context.Background()
	startTime := time.Now()
	err := defaultProducer.SendAsync(ctx, func(ctx context.Context, result *primitive.SendResult, err error) {
		if err != nil {
			fmt.Println(err)
			return
		}
		fmt.Println(result.MsgID)
	}, msg)
	fmt.Println("t: ", time.Since(startTime))
	return err
}

func main() {
	for i := 0; i < 20; i++ {
		sendMsg("your-topic-here", []byte("test-body1"))
	}
	time.Sleep(time.Second * 10)
	return
}