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/SubList/SubListQueueWeightTests.cs

@@ -0,0 +1,17 @@
+using NATS.Server.Subscriptions;
+
+namespace NATS.Server.Core.Tests;
+
+public class SubListQueueWeightTests
+{
+    [Fact]
+    public void Remote_queue_weight_expands_matches()
+    {
+        using var sl = new SubList();
+        sl.ApplyRemoteSub(new RemoteSubscription("orders.*", "q", "r1", "A", QueueWeight: 3));
+
+        var matches = sl.MatchRemote("A", "orders.created");
+        matches.Count.ShouldBe(3);
+        matches.ShouldAllBe(m => m.Queue == "q");
+    }
+}