feat: complete final jetstream parity transport and runtime baselines

tests/NATS.Server.Tests/JetStreamFlowReplayBackoffTests.cs

@@ -0,0 +1,15 @@
+using System.Diagnostics;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamFlowReplayBackoffTests
+{
+    [Fact]
+    public async Task Replay_original_respects_message_timestamps_with_backoff_redelivery()
+    {
+        await using var fx = await JetStreamApiFixture.StartWithReplayOriginalConsumerAsync();
+        var sw = Stopwatch.StartNew();
+        _ = await fx.FetchAsync("ORDERS", "RO", 1);
+        sw.ElapsedMilliseconds.ShouldBeGreaterThanOrEqualTo(50);
+    }
+}