task6(batch39): implement shutdown and signal flow paths

dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ImplBacklog/JetStreamClusterTests1.Impltests.cs

@@ -6,6 +6,33 @@ namespace ZB.MOM.NatsNet.Server.Tests.ImplBacklog;
 
 public sealed class JetStreamClusterTests1
 {
+    [Fact] // T:814
+    public void JetStreamClusterAccountPurge_ShouldSucceed()
+    {
+        var stream = NatsStream.Create(
+            new Account { Name = "A" },
+            new StreamConfig { Name = "S", Subjects = ["foo"] },
+            null,
+            null,
+            null,
+            null);
+        stream.ShouldNotBeNull();
+
+        var consumer = NatsConsumer.Create(stream!, new ConsumerConfig { Durable = "D" }, ConsumerAction.CreateOrUpdate, null);
+        consumer.ShouldNotBeNull();
+
+        consumer!.ApplyState(new ConsumerState
+        {
+            Pending = new Dictionary<ulong, Pending>
+            {
+                [1] = new Pending { Sequence = 1, Timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() },
+            },
+        });
+
+        consumer.Purge();
+        consumer.GetConsumerState().Pending.ShouldBeNull();
+    }
+
     [Fact] // T:772
     public void JetStreamClusterConsumerState_ShouldSucceed()
     {