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>

Test/E2E/suite/gen_data.py

@@ -113,6 +113,12 @@ def build_ground_truth(scenario):
                 "range_min": sig["range_min"], "range_max": sig["range_max"],
                 "is_time": sig["is_time"],
             }
+    hub = scenario.get("hub")
+    if hub and hub.get("mode") == "join":
+        # The merged stream carries every source signal as "<src>_<signal>".
+        for key in list(gt):
+            src_id, sig_name = key.split(":", 1)
+            gt[f"{hub['name']}:{src_id}_{sig_name}"] = gt[key]
     return gt