fix: start new connections independently of connection failures

[link2xt]

With current implementation
every time connection fails
we take the next delay from delays iterator.
In the worst case first 4 DNS results
immediately refuse connection
and we start fifth connection attempt
with 1 year timeout,
effectively continuing all remaining
connection attempts without concurrency.

With new implementation
new connection attempts are
added to connection_attempt_set
independently of connection failures
and after 10 seconds
we always end up with five
parallel connection attempts
as long as there are enough IP addresses.

[link2xt]

This is a follow-up to #5915. #5915 initially had similar implementation, but in second commit in the PR @Hocuri attempted to simplify the logic with using timeout and no tokio::select!. This PR reverts the simplification.