refactor: extract NATS.Server.JetStream.Tests project

Move 225 JetStream-related test files from NATS.Server.Tests into a
dedicated NATS.Server.JetStream.Tests project. This includes root-level
JetStream*.cs files, storage test files (FileStore, MemStore,
StreamStoreContract), and the full JetStream/ subfolder tree (Api,
Cluster, Consumers, MirrorSource, Snapshots, Storage, Streams).

Updated all namespaces, added InternalsVisibleTo, registered in the
solution file, and added the JETSTREAM_INTEGRATION_MATRIX define.

tests/NATS.Server.JetStream.Tests/JetStreamConsumerListApiTests.cs

@@ -0,0 +1,19 @@
+using NATS.Server.TestUtilities;
+
+namespace NATS.Server.JetStream.Tests;
+
+public class JetStreamConsumerListApiTests
+{
+    [Fact]
+    public async Task Consumer_names_list_and_delete_are_supported()
+    {
+        await using var fx = await JetStreamApiFixture.StartWithPullConsumerAsync();
+
+        var names = await fx.RequestLocalAsync("$JS.API.CONSUMER.NAMES.ORDERS", "{}");
+        names.ConsumerNames.ShouldNotBeNull();
+        names.ConsumerNames.ShouldContain("PULL");
+
+        var del = await fx.RequestLocalAsync("$JS.API.CONSUMER.DELETE.ORDERS.PULL", "{}");
+        del.Success.ShouldBeTrue();
+    }
+}