Performance: Optimistic DNS

I’m just gonna copy the description from AdGuard as they did a better job explaining this:

When the local DNS cache expires, NextDNS can continue answer with the IP in the local cache results with 1 TTL, while a new DNS query is made to update the cache. If client can still connect to the server by using the old results, then that's great and reduces the time waiting for DNS query. And if not, after a short TTL, the new DNS result can be sent to client and reconnect again.

This should, of cause, be implemented in the CLI