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

dotnet/src/ZB.MOM.NatsNet.Server/NatsServer.JetStreamCore.cs

@@ -424,4 +424,79 @@ public sealed partial class NatsServer
         var js = _jetStream;
         return js != null && Interlocked.CompareExchange(ref js.Disabled, 0, 0) == 0;
     }
+
+    public bool JetStreamEnabledForDomain()
+    {
+        if (JetStreamEnabled())
+            return true;
+
+        foreach (var value in _nodeToInfo.Values)
+        {
+            if (value is NodeInfo { Js: true })
+                return true;
+        }
+
+        return false;
+    }
+
+    public JetStreamConfig? JetStreamConfig()
+    {
+        var js = _jetStream;
+        if (js == null)
+            return null;
+
+        var cfg = js.Config;
+        return new JetStreamConfig
+        {
+            MaxMemory = cfg.MaxMemory,
+            MaxStore = cfg.MaxStore,
+            StoreDir = cfg.StoreDir,
+            SyncInterval = cfg.SyncInterval,
+            SyncAlways = cfg.SyncAlways,
+            Domain = cfg.Domain,
+            CompressOK = cfg.CompressOK,
+            UniqueTag = cfg.UniqueTag,
+            Strict = cfg.Strict,
+        };
+    }
+
+    public string StoreDir()
+    {
+        var js = _jetStream;
+        return js == null ? string.Empty : js.Config.StoreDir;
+    }
+
+    public int JetStreamNumAccounts()
+    {
+        var js = _jetStream;
+        if (js == null)
+            return 0;
+
+        js.Lock.EnterReadLock();
+        try
+        {
+            return js.Accounts.Count;
+        }
+        finally
+        {
+            js.Lock.ExitReadLock();
+        }
+    }
+
+    public (long MemReserved, long StoreReserved, Exception? Error) JetStreamReservedResources()
+    {
+        var js = _jetStream;
+        if (js == null)
+            return (-1, -1, new InvalidOperationException("jetstream not enabled"));
+
+        return (
+            Interlocked.Read(ref js.MemReserved),
+            Interlocked.Read(ref js.StoreReserved),
+            null);
+    }
+
+    internal JetStreamEngine? GetJetStream() =>
+        _jetStream == null ? null : new JetStreamEngine(_jetStream);
+
+    internal JetStream? GetJetStreamState() => _jetStream;
 }