feat: add jetstream mirror and source orchestration

tests/NATS.Server.Tests/JetStreamMirrorSourceTests.cs

@@ -0,0 +1,16 @@
+namespace NATS.Server.Tests;
+
+public class JetStreamMirrorSourceTests
+{
+    [Fact]
+    public async Task Mirror_stream_replays_origin_messages()
+    {
+        await using var fixture = await JetStreamApiFixture.StartWithMirrorSetupAsync();
+
+        await fixture.PublishAndGetAckAsync("ORDERS", "orders.created", "1");
+        await fixture.WaitForMirrorSyncAsync("ORDERS_MIRROR");
+
+        var state = await fixture.GetStreamStateAsync("ORDERS_MIRROR");
+        state.Messages.ShouldBe((ulong)1);
+    }
+}