adds DNS.OverrideSystem flag (enabled by default) that extends
DNS.Resolvers to affect all DNS lookups in the daemon process,
not just DNSLink and Multiaddr resolution.
this ensures AutoTLS ACME DNS-01 challenge verification, HTTP retrieval,
and third-party library code all respect DNS.Resolvers config.
implementation creates a net.Resolver bridge that intercepts DNS wire
protocol queries, parses them with miekg/dns, calls madns.Resolver,
and returns properly formatted DNS responses.
note: this is an exploration of daemon-wide DNS configuration without
refactoring boxo/gateway. a cleaner future approach may create native
net.Resolver from config first, then convert to madns only for go-libp2p.
541bd657a6