feat: complete remaining jetstream parity implementation plan

tests/NATS.Server.Tests/JetStreamPullConsumerContractTests.cs

@@ -0,0 +1,14 @@
+namespace NATS.Server.Tests;
+
+public class JetStreamPullConsumerContractTests
+{
+    [Fact]
+    public async Task Pull_fetch_no_wait_returns_immediately_when_empty()
+    {
+        await using var fx = await JetStreamApiFixture.StartWithPullConsumerAsync();
+
+        var batch = await fx.FetchWithNoWaitAsync("ORDERS", "PULL", batch: 1);
+        batch.Messages.Count.ShouldBe(0);
+        batch.TimedOut.ShouldBeFalse();
+    }
+}