Dial timeout error still is not redirectable

[vladisa88]

After we fix #3786

I think that we haven't finished with this bug yet. I've updated lib version, decided to re-check and noticed that dial tcp timeouts still not redirectable. So I think that problem is here

# internal/pool/pool.go
attemptCtx, cancel = context.WithTimeout(ctx, p.cfg.DialTimeout)

We use context timeout here. So when dial timeout is over *net.OpError{Op: "dial"} is wrapped inside ContextDeadlineExceeded, so in shouldRetry this condition is true

if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
	return false
}

I suppose that we should move new condition before this check

var opErr *net.OpError
if errors.As(err, &opErr) && opErr.Op == "dial" {
    return true 
}

if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
	return false
}

@ndyakov Hi! I commented in original issue #3799 (comment) so we can reopen it or discuss it here

[ndyakov]

Hello @vladisa88. Thanks for testing. Maybe prepare a unit test and let's try the suggested approach.

[vladisa88]

Okey, I'll do it