refactor: rename remaining tests to NATS.Server.Core.Tests

- Rename tests/NATS.Server.Tests -> tests/NATS.Server.Core.Tests
- Update solution file, InternalsVisibleTo, and csproj references
- Remove JETSTREAM_INTEGRATION_MATRIX and NATS.NKeys from csproj (moved to JetStream.Tests and Auth.Tests)
- Update all namespaces from NATS.Server.Tests.* to NATS.Server.Core.Tests.*
- Replace private GetFreePort/ReadUntilAsync helpers with TestUtilities calls
- Fix stale namespace in Transport.Tests/NetworkingGoParityTests.cs

tests/NATS.Server.Core.Tests/Subscriptions/SubListParityBatch2Tests.cs

@@ -0,0 +1,130 @@
+using NATS.Server;
+using NATS.Server.Auth;
+using NATS.Server.Protocol;
+using NATS.Server.Subscriptions;
+
+namespace NATS.Server.Core.Tests.Subscriptions;
+
+public class SubListParityBatch2Tests
+{
+    [Fact]
+    public void RegisterQueueNotification_tracks_first_and_last_exact_queue_interest()
+    {
+        var subList = new SubList();
+        var notifications = new List<bool>();
+        Action<bool> callback = hasInterest => notifications.Add(hasInterest);
+
+        subList.RegisterQueueNotification("foo.bar", "q", callback).ShouldBeTrue();
+        notifications.ShouldBe([false]);
+
+        var sub1 = new Subscription { Subject = "foo.bar", Queue = "q", Sid = "1" };
+        var sub2 = new Subscription { Subject = "foo.bar", Queue = "q", Sid = "2" };
+
+        subList.Insert(sub1);
+        subList.Insert(sub2);
+        notifications.ShouldBe([false, true]);
+
+        subList.Remove(sub1);
+        notifications.ShouldBe([false, true]);
+
+        subList.Remove(sub2);
+        notifications.ShouldBe([false, true, false]);
+
+        subList.ClearQueueNotification("foo.bar", "q", callback).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void UpdateRemoteQSub_updates_queue_weight_for_match_remote()
+    {
+        var subList = new SubList();
+        var original = new RemoteSubscription("foo.bar", "q", "R1", Account: "A", QueueWeight: 1);
+        subList.ApplyRemoteSub(original);
+        subList.MatchRemote("A", "foo.bar").Count.ShouldBe(1);
+
+        subList.UpdateRemoteQSub(original with { QueueWeight = 3 });
+        subList.MatchRemote("A", "foo.bar").Count.ShouldBe(3);
+    }
+
+    [Fact]
+    public void SubListStats_Add_aggregates_stats_like_go()
+    {
+        var stats = new SubListStats
+        {
+            NumSubs = 1,
+            NumCache = 2,
+            NumInserts = 3,
+            NumRemoves = 4,
+            NumMatches = 10,
+            MaxFanout = 5,
+            TotalFanout = 8,
+            CacheEntries = 2,
+            CacheHits = 6,
+        };
+
+        stats.Add(new SubListStats
+        {
+            NumSubs = 2,
+            NumCache = 3,
+            NumInserts = 4,
+            NumRemoves = 5,
+            NumMatches = 30,
+            MaxFanout = 9,
+            TotalFanout = 12,
+            CacheEntries = 3,
+            CacheHits = 15,
+        });
+
+        stats.NumSubs.ShouldBe((uint)3);
+        stats.NumCache.ShouldBe((uint)5);
+        stats.NumInserts.ShouldBe((ulong)7);
+        stats.NumRemoves.ShouldBe((ulong)9);
+        stats.NumMatches.ShouldBe((ulong)40);
+        stats.MaxFanout.ShouldBe((uint)9);
+        stats.AvgFanout.ShouldBe(4.0);
+        stats.CacheHitRate.ShouldBe(0.525);
+    }
+
+    [Fact]
+    public void NumLevels_returns_max_trie_depth()
+    {
+        var subList = new SubList();
+        subList.Insert(new Subscription { Subject = "foo.bar.baz", Sid = "1" });
+        subList.Insert(new Subscription { Subject = "foo.bar", Sid = "2" });
+
+        subList.NumLevels().ShouldBe(3);
+    }
+
+    [Fact]
+    public void LocalSubs_filters_non_local_kinds_and_optionally_includes_leaf()
+    {
+        var subList = new SubList();
+        subList.Insert(new Subscription { Subject = "foo.a", Sid = "1", Client = new TestClient(ClientKind.Client) });
+        subList.Insert(new Subscription { Subject = "foo.b", Sid = "2", Client = new TestClient(ClientKind.Router) });
+        subList.Insert(new Subscription { Subject = "foo.c", Sid = "3", Client = new TestClient(ClientKind.System) });
+        subList.Insert(new Subscription { Subject = "foo.d", Sid = "4", Client = new TestClient(ClientKind.Leaf) });
+
+        var local = subList.LocalSubs(includeLeafHubs: false).Select(s => s.Sid).OrderBy(x => x).ToArray();
+        local.ShouldBe(["1", "3"]);
+
+        var withLeaf = subList.LocalSubs(includeLeafHubs: true).Select(s => s.Sid).OrderBy(x => x).ToArray();
+        withLeaf.ShouldBe(["1", "3", "4"]);
+    }
+
+    private sealed class TestClient(ClientKind kind) : INatsClient
+    {
+        public ulong Id => 1;
+        public ClientKind Kind => kind;
+        public Account? Account => null;
+        public ClientOptions? ClientOpts => null;
+        public ClientPermissions? Permissions => null;
+        public void SendMessage(string subject, string sid, string? replyTo, ReadOnlyMemory<byte> headers, ReadOnlyMemory<byte> payload)
+        {
+        }
+
+        public bool QueueOutbound(ReadOnlyMemory<byte> data) => true;
+
+        public void RemoveSubscription(string sid)
+        {
+        }
+    }
+}