This effectively means that `doggo @2001:DB8::53 example.org` works just
like we know it from `dig(1)`. This already works for IPv4 because
`url.Parse` accepts a literal IPv4 address, but not a literal IPv6
address (due to parsing ambiguities with strings that look like an IPv4
address I guess).
This is implemented by checking if the nameserver argument is a valid IP
if the URL validation failed. If that's the case, `ns` is returned
directly with the `[2001:DB8::53]:53` as address (from
`net.JoinHostPort` with the default DNS port) and UDP as protocol (also
the default if not specified).
