When DNS_REAL_RECURSIVE=true and DNS_ZONE_MODE=recursive, out-of-zone
queries are forwarded to DNS_UPSTREAM (default 8.8.8.8:53) via async
UDP. Upstream response is relayed as-is; on timeout or error the
already-computed sinkhole (127.x) is returned instead.
_handle() always runs first so logging, tunneling detection, flood
tracking, and recon-burst aggregation fire on every query regardless
of whether the response ultimately comes from upstream. _dispatch()
overlays forwarding on top of the sync handler.
Protocol handlers (UDP datagram_received, TCP session) are now async
via asyncio.ensure_future / await _dispatch(). Service class exposes
real_recursive (bool) and upstream (string) config fields.