feat: add JoeAppEngine OPC UA nodes, fix DCL auto-reconnect and quality push

- Add JoeAppEngine folder to OPC UA nodes.json (BTCS, AlarmCntsBySeverity, Scheduler/ScanTime)
- Fix DataConnectionActor: capture Self in PreStart for use from non-actor threads,
  preventing Self.Tell failure in Disconnected event handler
- Implement InstanceActor.HandleConnectionQualityChanged to mark attributes Bad on disconnect
- Fix LmxFakeProxy TagMapper to serialize arrays as JSON instead of "System.Int32[]"
- Allow DataType and DataSourceReference updates in TemplateService.UpdateAttributeAsync
- Update test_infra_opcua.md with JoeAppEngine documentation

infra/lmxfakeproxy/TagMapper.cs

@@ -1,3 +1,5 @@
+using System.Collections;
+using System.Text.Json;
 using LmxFakeProxy.Grpc;
 
 namespace LmxFakeProxy;
@@ -30,12 +32,20 @@ public class TagMapper
         return "Uncertain";
     }
 
+    public static string FormatValue(object? value)
+    {
+        if (value is null) return string.Empty;
+        if (value is Array or IList)
+            return JsonSerializer.Serialize(value);
+        return value.ToString() ?? string.Empty;
+    }
+
     public static VtqMessage ToVtqMessage(string tag, object? value, DateTime timestampUtc, uint statusCode)
     {
         return new VtqMessage
         {
             Tag = tag,
-            Value = value?.ToString() ?? string.Empty,
+            Value = FormatValue(value),
             TimestampUtcTicks = timestampUtc.Ticks,
             Quality = MapQuality(statusCode)
         };