feat: optimize connection pool waitTurn (#3412)

Author: twz915

internal/pool/pool.go

@@ -325,25 +325,23 @@ func (p *ConnPool) waitTurn(ctx context.Context) error {
 
 	start := time.Now()
 	timer := timers.Get().(*time.Timer)
+	defer timers.Put(timer)
 	timer.Reset(p.cfg.PoolTimeout)
 
 	select {
 	case <-ctx.Done():
 		if !timer.Stop() {
 			<-timer.C
 		}
-		timers.Put(timer)
 		return ctx.Err()
 	case p.queue <- struct{}{}:
 		p.waitDurationNs.Add(time.Since(start).Nanoseconds())
 		atomic.AddUint32(&p.stats.WaitCount, 1)
 		if !timer.Stop() {
 			<-timer.C
 		}
-		timers.Put(timer)
 		return nil
 	case <-timer.C:
-		timers.Put(timer)
 		atomic.AddUint32(&p.stats.Timeouts, 1)
 		return ErrPoolTimeout
 	}