feat: standalone C/C++ UDPS client library

Consuming a UDPStreamer feed so far meant either linking MARTe2 (UDPSClient)
or writing Go (Common/Client/go/udpsprotocol). Common/Client/c fills the gap
for plain C/C++ integrators: two files depending on nothing but libc and BSD
sockets, covering the whole receive path — CONNECT, fragment reassembly,
CONFIG/DATA decoding with dequantisation, keepalives and silence-triggered
reconnect. No threads are spawned; udps_client_poll() does all the work and
runs every callback, so it drops into an existing event loop unsynchronised.

Verified against run_udp_producer.sh at 1 Msps: unicast (120 MiB, no loss) and
multicast with 12-fragment cycles (116k datagrams, no loss).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -244,6 +244,7 @@ Open `http://localhost:9090`, explore the object tree, trace signals, force valu
 | ----------------------------- | -------------------------------------------------------------- |
 | `Docs/Protocol.md`            | UDPS binary wire protocol specification                        |
 | `Docs/UDPStreamer.md`         | UDPStreamer DataSource configuration reference                 |
+| `Docs/UDPS-C-Client.md`       | Standalone C/C++ UDPS receiver library (`Common/Client/c`)     |
 | `Docs/SineArrayGAM.md`        | SineArrayGAM configuration reference                           |
 | `Docs/DebugService.md`        | DebugService TCP API and architecture                          |
 | `Docs/Tutorial.md`            | Step-by-step tutorial covering both components                 |