feat(batch27): implement jetstream engine state and account enable core

dotnet/src/ZB.MOM.NatsNet.Server/JetStream/JetStreamEngine.cs

@@ -0,0 +1,47 @@
+namespace ZB.MOM.NatsNet.Server;
+
+internal sealed class JetStreamEngine(JetStream state)
+{
+    private readonly JetStream _state = state;
+
+    internal void SetStarted()
+    {
+        _state.Lock.EnterWriteLock();
+        try
+        {
+            _state.Started = DateTime.UtcNow;
+        }
+        finally
+        {
+            _state.Lock.ExitWriteLock();
+        }
+    }
+
+    internal bool IsEnabled() => Interlocked.CompareExchange(ref _state.Disabled, 0, 0) == 0;
+
+    internal void SetJetStreamStandAlone(bool isStandAlone)
+    {
+        _state.Lock.EnterWriteLock();
+        try
+        {
+            _state.StandAlone = isStandAlone;
+        }
+        finally
+        {
+            _state.Lock.ExitWriteLock();
+        }
+    }
+
+    internal bool IsShuttingDown()
+    {
+        _state.Lock.EnterReadLock();
+        try
+        {
+            return _state.ShuttingDown;
+        }
+        finally
+        {
+            _state.Lock.ExitReadLock();
+        }
+    }
+}