Add dual-stack (IPv4/IPv6) support to node-cache

Problem:

In dual-stack clusters, node-cache (node-local-dns) only handles a single IP family. IPv6 DNS queries bypass the local cache entirely, which defeats the cache's performance and reliability benefits — and can cause unexpected failover (e.g. nslookup falling back to an IPv6 nameserver that isn't intercepted).

Proposal:

Extend node-cache to handle IPv4 and IPv6 traffic simultaneously, so DNS queries from both families are served by the local cache in dual-stack clusters.

Start by tracing node-cache (node-local-dns) to find where it selects a single IP family and how DNS queries are intercepted. Done means IPv4 and IPv6 queries are both served by the local cache in dual-stack clusters, with behavior verified for the reported failover case.

Written by the indexing model from the issue text.