feat: execute post-baseline jetstream parity plan

src/NATS.Server/JetStream/ConsumerManager.cs

@@ -157,6 +157,10 @@ public sealed class ConsumerManager
         if (consumer.PushFrames.Count == 0)
             return null;
 
+        var frame = consumer.PushFrames.Peek();
+        if (frame.AvailableAtUtc > DateTime.UtcNow)
+            return null;
+
         return consumer.PushFrames.Dequeue();
     }
 
@@ -179,4 +183,5 @@ public sealed record ConsumerHandle(string Stream, ConsumerConfig Config)
     public Queue<StoredMessage> Pending { get; } = new();
     public Queue<PushFrame> PushFrames { get; } = new();
     public AckProcessor AckProcessor { get; } = new();
+    public DateTime NextPushDataAvailableAtUtc { get; set; }
 }