use of closed network connection occurs rarely when context is canceled during establishing a connection

[yokonao]

Issue description

Executing query returns context.Canceled in most cases when context canceled.
However, we see use of closed network connection rarely when context canceled during querying or executing.

For error handling purposes, it is preferable to always return context.Canceled.

similar issue: #1078

Example code

package main

import (
	"context"
	"errors"
	"log"
	"os"
	"time"

	"github.com/go-sql-driver/mysql"
)

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	dsn := "mysql:" + os.Getenv("DB_PASSWD") + "@tcp(127.0.0.1:3306)/?allowNativePasswords=true&tls=preferred"
	connector, err := mysql.MySQLDriver{}.OpenConnector(dsn)
	if err != nil {
		log.Fatal(err)
	}

	go func() {
		time.Sleep(10 * time.Millisecond) // may be need to adjust the sleep time.
		cancel()
	}()
	conn, err := connector.Connect(ctx)
	if err != nil {
		if errors.Is(err, context.Canceled) {
			log.Println("context canceled. no problem.")
			return
		}
		panic(err) // use of closed network connection
	}
	defer conn.Close()
}

It seems that use of closed network connection occurs when ctx is canceled at a specific timing while the connection is being established.

Error log

panic: read tcp 127.0.0.1:51710->127.0.0.1:3306: use of closed network connection

Configuration

Driver version (or git SHA): v1.7.1 f20b286
Go version: go version go1.22.4 darwin/arm64
Server version: Mysql 8.0

Server OS: Debian GNU/Linux 11 (bullseye)