TraceHop.asn/as_name existed in the model since the start but nothing ever
populated them. New probes/hop_asn.py fires one Team Cymru DNS query pair
per unique hop IP (in-run deduped, no rate limit unlike the cached_json()
providers) after the latency/path/TLS fan-out, plus a PTR lookup for hops
whose reverse_dns is still empty because the backend that produced them
doesn't resolve hostnames itself (icmp_win/icmplib/mtr, unlike system
traceroute text).
New path.detour_country finding flags a route that spends two or more
consecutive hops in a country that's neither the client's nor the
destination's. Wires up providers.cymru_asn_zone, which was configured but
referenced nowhere, and adds cymru_origin6_zone for the IPv6 branch Phase 8
will need.
Part of plans/zesty-zooming-wilkinson.md (gitignored).
