Implement worker heartbeat watchdog

src/MxGateway.Worker/MxAccess/WorkerRuntimeHeartbeatSnapshot.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace MxGateway.Worker.MxAccess;
+
+public sealed class WorkerRuntimeHeartbeatSnapshot
+{
+    public WorkerRuntimeHeartbeatSnapshot(
+        DateTimeOffset lastStaActivityUtc,
+        uint pendingCommandCount,
+        uint outboundEventQueueDepth,
+        ulong lastEventSequence,
+        string currentCommandCorrelationId)
+    {
+        LastStaActivityUtc = lastStaActivityUtc;
+        PendingCommandCount = pendingCommandCount;
+        OutboundEventQueueDepth = outboundEventQueueDepth;
+        LastEventSequence = lastEventSequence;
+        CurrentCommandCorrelationId = currentCommandCorrelationId ?? string.Empty;
+    }
+
+    public DateTimeOffset LastStaActivityUtc { get; }
+
+    public uint PendingCommandCount { get; }
+
+    public uint OutboundEventQueueDepth { get; }
+
+    public ulong LastEventSequence { get; }
+
+    public string CurrentCommandCorrelationId { get; }
+}