feat: support connection pool level client session

[hantmac]

re-produce code:

package main

import (
	"database/sql"
	"sync"

	_ "github.com/datafuselabs/databend-go"
)

func main() {
	conn, err := sql.Open("databend", "http://databend:databend@localhost:8009/default?sslmode=disable")
	if err != nil {
		panic(err)
	}

	conn.SetMaxIdleConns(3)
	conn.SetMaxOpenConns(3)

	_, err = conn.Exec("set enable_query_result_cache = 1;")
	if err != nil {
		panic(err)
	}

	var wg sync.WaitGroup
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			rows, err := conn.Query("select value, default from system.settings where name = 'enable_query_result_cache'")
			if err != nil {
				panic(err)
			}
			for rows.Next() {
				var value string
				var defaultValue string
				if err := rows.Scan(&value, &defaultValue); err != nil {
					panic(err)
				}
				println("loop", i, "  value -->", value, "default -->", defaultValue)
			}
		}(i)
	}
	wg.Wait()

}

In connection pool, the conn should use the same session state info.