Add TCP, UDP, and WebSocket output servers

[junzis]

Summary

• Add output servers to serve decoded AIS messages as timestamped NMEA (Norwegian coast guard IEC 61162-1 format) via TCP, UDP, and WebSocket
• This allows ship162 to decode from SDR and re-broadcast to downstream consumers as if they were connecting to the Norwegian Coastal Administration feed
• New config options: serve_tcp, serve_udp, serve_ws, udp_targets

Details

TCP server (outputs/tcp.rs): Clients connect and receive a continuous NMEA stream. Uses tokio::sync::broadcast for fan-out to multiple clients with automatic cleanup on disconnect.

UDP server (outputs/udp.rs): Supports both static targets (configured via udp_targets) and dynamic peer registration (clients send any datagram to register). Useful for pushing data to remote hosts.

WebSocket server (outputs/websocket.rs): Clients connect via ws:// and receive NMEA messages. Built on tokio-tungstenite.

NMEA encoding (outputs/mod.rs): Formats messages with Norwegian coast guard timestamp tag blocks: \s:SERIAL,c:TIMESTAMP*CHECKSUM\!AIVDM,...

SDR-decoded messages now call encode_nmea() to generate NMEA sentences before sending through the pipeline.

Configuration example

serve_tcp = "0.0.0.0:5631"
serve_ws = "0.0.0.0:8080"
udp_targets = ["x.x.x.x:88888"]

[[sources]]
soapy.args="driver=sdrplay"
soapy.sample_rate=1000000
gain=50

New dependencies

• tokio-tungstenite (WebSocket protocol)

Test plan

• TCP output: verified with nc localhost 5631 — receives live NMEA stream from SDRplay RSPdxR2
• UDP output: verified with Python UDP listener — receives NMEA datagrams
• WebSocket: verified handshake with curl
• cargo fmt — clean
• cargo clippy — zero warnings
• Release build with --features soapy — passes
• Tested live on sil server with SDRplay RSPdxR2 antenna