style(worker-tests): field ordering in FakeRuntimeSession

refreshStaActivityOnCapture was declared between DispatchAsync and the property that
wraps it, rather than with the other instance fields. Moved up to the field block per the
member ordering in docs/style-guides/CSharpStyleGuide.md. Declaration move only — no
behavior, no other edits.

src/ZB.MOM.WW.MxGateway.Worker.Tests/TestSupport/FakeRuntimeSession.cs

@@ -42,6 +42,7 @@ internal sealed class FakeRuntimeSession : IWorkerRuntimeSession
     // disposed SemaphoreSlim would turn that shutdown into an ObjectDisposedException.
     private readonly SemaphoreSlim eventSignal = new(0, 1);
     private TimeSpan? lastWaitForEventsTimeout;
+    private bool refreshStaActivityOnCapture;
     private WorkerRuntimeHeartbeatSnapshot snapshot = new(
         DateTimeOffset.UtcNow,
         pendingCommandCount: 0,
@@ -138,8 +139,6 @@ internal sealed class FakeRuntimeSession : IWorkerRuntimeSession
             });
     }
 
-    private bool refreshStaActivityOnCapture;
-
     /// <summary>
     ///     When set, <see cref="CaptureHeartbeat"/> stamps the snapshot's
     ///     <c>LastStaActivityUtc</c> with the capture time and leaves every other field as the last