CVE-2026-32934: CoreDNS' DoQ worker pool does not bound stream backlog

CoreDNS’ DNS-over-QUIC (DoQ) server can be driven into large goroutine and memory growth by a remote client that opens many QUIC streams and stalls after sending only 1 byte. Even with a small configured quic { worker_pool_size … }, CoreDNS still spawns a goroutine per accepted stream (workers + waiters) and active workers can block indefinitely in io.ReadFull() with no per-stream read deadline, enabling unauthenticated remote DoS via memory exhaustion/OOM-kill.