feat: complete remaining jetstream parity implementation plan

tests/NATS.Server.Tests/JetStreamClusterControlApiTests.cs

@@ -0,0 +1,19 @@
+namespace NATS.Server.Tests;
+
+public class JetStreamClusterControlApiTests
+{
+    [Fact]
+    public async Task Stream_leader_stepdown_and_meta_stepdown_endpoints_return_success_shape()
+    {
+        await using var fx = await JetStreamClusterFixture.StartAsync(nodes: 3);
+
+        var create = await fx.CreateStreamAsync("ORDERS", replicas: 3);
+        create.Error.ShouldBeNull();
+
+        var streamStepdown = await fx.RequestAsync("$JS.API.STREAM.LEADER.STEPDOWN.ORDERS", "{}");
+        streamStepdown.Success.ShouldBeTrue();
+
+        var metaStepdown = await fx.RequestAsync("$JS.API.META.LEADER.STEPDOWN", "{}");
+        metaStepdown.Success.ShouldBeTrue();
+    }
+}