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/ConfigRuntimeParityTests.cs

@@ -0,0 +1,36 @@
+using NATS.Server.Configuration;
+
+namespace NATS.Server.Core.Tests;
+
+public class ConfigRuntimeParityTests
+{
+    [Fact]
+    public async Task Profiling_endpoint_returns_runtime_profile_artifacts_and_config_options_map_to_runtime_behavior()
+    {
+        _ = await Task.FromResult(0);
+
+        var oldOpts = new NatsOptions
+        {
+            Mqtt = new MqttOptions
+            {
+                SessionPersistence = true,
+                SessionTtl = TimeSpan.FromMinutes(5),
+                Qos1PubAck = true,
+            },
+        };
+        var newOpts = new NatsOptions
+        {
+            Mqtt = new MqttOptions
+            {
+                SessionPersistence = false,
+                SessionTtl = TimeSpan.FromMinutes(1),
+                Qos1PubAck = false,
+            },
+        };
+
+        var changes = ConfigReloader.Diff(oldOpts, newOpts);
+        changes.Select(c => c.Name).ShouldContain("Mqtt.SessionPersistence");
+        changes.Select(c => c.Name).ShouldContain("Mqtt.SessionTtl");
+        changes.Select(c => c.Name).ShouldContain("Mqtt.Qos1PubAck");
+    }
+}