feat(tcp): TCPStreamer DataSources, in-process TCPStreamService, stream multiplexing and TCPStreamJoin

Add TCPStreamer/TCPStreamerClient (TCP transport behind the UDPSServerI/UDPSClientI
seam), an optional single in-process TCPStreamService serving many streams over
worker threads, multiplexed SUBSCRIBE (comma list, stream index in fragmentIdx),
and TCPStreamJoin, which merges several streams into one sample-and-hold stream
paced by a master. StreamHub takes a comma list of streams over one connection.
Includes GTests, E2E scenarios s58-s73 and docs.

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

Source/Components/DataSources/UDPStreamer/UDPStreamer.h

@@ -39,6 +39,7 @@
 #include "SingleThreadService.h"
 #include "StreamString.h"
 #include "UDPSServer.h"
+#include "UDPSTransportI.h"
 
 /*---------------------------------------------------------------------------*/
 /*                           Class declaration                               */
@@ -333,6 +334,33 @@ public:
      */
     uint32 GetDroppedPublications() const;
 
+protected:
+    /**
+     * @brief MaxPayloadSize used when the configuration does not specify one.
+     * @details Transport specific (a datagram budget for UDP, a frame budget for
+     * TCP), hence overridable. Called from Initialise(), not the constructor.
+     */
+    virtual uint32 DefaultMaxPayloadSize() const;
+
+    /**
+     * @brief Configures the transport from the already-resolved Port and
+     * MaxPayloadSize plus whatever transport keys @p data carries.
+     * @details The default implementation configures the UDPSServer (unicast /
+     * multicast). A subclass that installs another transport with SetServer()
+     * overrides this to configure it instead.
+     */
+    virtual bool InitialiseTransport(StructuredDataI &data);
+
+    /**
+     * @brief Replaces the transport. Takes ownership; only valid before Start().
+     */
+    void SetServer(UDPSServerI *newServer);
+
+    /**
+     * @brief The transport currently in use (owned by this object).
+     */
+    UDPSServerI *Transport() const;
+
 private:
     /**
      * @brief Serializes the CONFIG payload into buf and sets payloadSize.
@@ -417,8 +445,8 @@ private:
     uint8  *wireBuffer;      /**< Pre-allocated buffer for the serialized DATA payload */
     uint32  totalWireBytes;  /**< Total bytes of all signals after quantization + 8-byte timestamp prefix */
 
-    /* Networking — handled by UDPSServer */
-    UDPSServer      server;          /**< Multi-client session manager (unicast and multicast) */
+    /* Networking — handled by a UDPSServerI (UDPSServer by default) */
+    UDPSServerI    *server;          /**< Owned transport; see SetServer() */
 
     /* Thread management */
     SingleThreadService executor;    /**< Background thread service */