Adds 22 DNS e2e subtests across 8 test methods covering: upstream
resolution (A, AAAA, multi-A), TCP mode, bypass rules, host mapper,
exchange failure (graceful error recovery), rate limiter wiring,
invalid query handling, and DNS over TLS (mode: tls).
Includes two authoritative DNS responders (UDP/TCP), a standalone
DNS query client, and a TLS DNS query script.
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