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/UDPStreamerClient/UDPStreamerClient.h

@@ -160,6 +160,27 @@ public:
      */
     virtual void OnUDPSDisconnected();
 
+protected:
+    /**
+     * @brief Configures the transport from the already-parsed members and
+     * registers this object as its listener.
+     * @details The default implementation configures the UDPSClient (unicast /
+     * multicast). A subclass that installs another transport with SetClient()
+     * overrides this to configure it instead.
+     */
+    virtual bool InitialiseTransport(StructuredDataI &data);
+
+    /**
+     * @brief Replaces the transport. Takes ownership; only valid before Start().
+     */
+    void SetClient(UDPSClientI *newClient);
+
+    /* Configuration parameters shared with transport subclasses */
+    StreamString serverAddress;  /**< Server IP address. */
+    uint16       port;           /**< Server port. */
+    uint32       cpuMask;        /**< Background thread CPU affinity. */
+    uint32       stackSize;      /**< Background thread stack size. */
+
 private:
     /**
      * @brief Decodes a single snapshot from a DATA payload into @p dst.
@@ -171,13 +192,9 @@ private:
     void DecodeSnapshot(const uint8 *payload, uint32 size, uint8 *dst);
 
     /* Configuration parameters */
-    StreamString serverAddress;  /**< Server IP address. */
-    uint16       port;           /**< Server port. */
     uint32       maxPayloadSize; /**< Max payload bytes per datagram. */
     uint32       keepAliveInterval; /**< Seconds between unicast keepalive ACKs (0 disables). */
     float32      silenceTimeout;    /**< Seconds of no data before reconnect (sub-second allowed, 0 disables). */
-    uint32       cpuMask;        /**< Background thread CPU affinity. */
-    uint32       stackSize;      /**< Background thread stack size. */
     StreamString multicastGroup;         /**< Multicast group IP; empty = unicast. */
     StreamString multicastInterface;     /**< Local IPv4 address for multicast join; empty = INADDR_ANY. */
     uint16       dataPort;               /**< UDP port for DATA datagrams (multicast). */
@@ -191,7 +208,7 @@ private:
     uint8                    publishMode;   /**< UDPS_PUBLISH_* from CONFIG. */
 
     /* Shared receiver (same code base as the StreamHub hub) */
-    UDPSClient client;      /**< Transport, reassembly and reconnect. */
+    UDPSClientI *client;    /**< Owned transport (UDPSClient by default); see SetClient(). */
     bool       receiverUp;  /**< True once the receiver thread is started. */
 
     /* Double-buffering for RT safety */