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>

Common/Client/c/Makefile

@@ -0,0 +1,46 @@
+# UDPS C client library — standalone, no MARTe2, no external dependencies.
+#
+#   make           build libudpsclient.a and the example
+#   make example   build only the example
+#   make cxxcheck  verify the header is usable from C++
+#   make clean
+
+CC      ?= cc
+CXX     ?= c++
+AR      ?= ar
+CFLAGS  ?= -O2 -g
+WARN     = -Wall -Wextra -Wpedantic
+STD      = -std=c99
+CPPFLAGS += -I.
+
+# Old glibc (< 2.17) keeps clock_gettime in librt; harmless to add there.
+LDLIBS ?=
+
+LIB     = libudpsclient.a
+OBJ     = udps_client.o
+EXAMPLE = udps_dump
+
+.PHONY: all example cxxcheck clean
+
+all: $(LIB) $(EXAMPLE)
+
+$(LIB): $(OBJ)
+	$(AR) rcs $@ $^
+
+udps_client.o: udps_client.c udps_client.h
+	$(CC) $(STD) $(WARN) $(CFLAGS) $(CPPFLAGS) -c -o $@ $<
+
+example: $(EXAMPLE)
+
+$(EXAMPLE): example/udps_dump.c $(LIB)
+	$(CC) $(STD) $(WARN) $(CFLAGS) $(CPPFLAGS) -o $@ $< $(LIB) $(LDLIBS)
+
+# The header is C++-safe; this target keeps it that way.
+cxxcheck: udps_client.h
+	echo '#include "udps_client.h"' > .cxxcheck.cpp
+	echo 'int main() { udps_client_config_t c; udps_client_config_init(&c); return 0; }' >> .cxxcheck.cpp
+	$(CXX) -std=c++11 -Wall -Wextra $(CPPFLAGS) -o .cxxcheck .cxxcheck.cpp $(LIB) $(LDLIBS)
+	./.cxxcheck && rm -f .cxxcheck .cxxcheck.cpp
+
+clean:
+	rm -f $(LIB) $(OBJ) $(EXAMPLE) .cxxcheck .cxxcheck.cpp