Discover AirPlay/RAOP receivers on the LAN via mDNS (multicast DNS, 224.0.0.251:5353) — the Bonjour service browse Apple devices use. Queries the _raop._tcp.local service and resolves each instance's SRV (host/port) + A (address) from the responses.

AirPlay is a different discovery + streaming stack. Returns %{name: String.t(), host: String.t(), port: non_neg_integer()} per receiver, plus any advertised TXT metadata such as :txt, :model_identifier, :model, :manufacturer, :features, :source_version, :os_version, :protocol_version, and :airplay_protocol.