test(mqtt): pin status-code half of republish suppression; note Sparkplug bypass

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttSubscriptionManager.cs

@@ -755,6 +755,10 @@ public sealed class MqttSubscriptionManager
         // sink write) per message. The cache is still freshened — a read must serve the current
         // timestamp — and only the notification is skipped. "Cached but not raised" is already a valid
         // state on this path (see Raise: an authored-but-unsubscribed tag does exactly that).
+        //
+        // Sparkplug bypasses this entirely. SparkplugIngestor.cs updates Values and raises directly
+        // (its own Values.Update()/Raise() calls, not through this Deliver method), so Sparkplug B
+        // ingestion gets no unchanged-value suppression — deliberately out of scope here.
         var prior = Values.Read(def.Name);
         var unchanged = prior.StatusCode == snapshot.StatusCode && !ValuesAreDifferent(prior.Value, snapshot.Value);