* feat(netxlite): support extracting the CNAME
Closes https://github.com/ooni/probe/issues/2225
* fix(netxlite): attempt to increase coverage and improve tests
1. dnsovergetaddrinfo: specify the behavior of a DNSResponse returned
by this file to make it line with normal responses and write unit tests
to make sure we adhere to expectations;
2. dnsoverudp: make sure we wait to deferred responses also w/o a
custom context and post on a private channel and test that;
3. utls: recognize that we can actually write a test for NetConn and
what needs to change when we'll use go1.19 by default will just be
a cast that at that point can be removed.
cc24f28b9d