test(batch48): add integration test harness infrastructure

Create 7 helper files under ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/
and add Xunit.SkippableFact package. All tests skip gracefully via
IntegrationTestBase.CanBoot() guard until the .NET server runtime is complete.

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/NatsTestClient.cs

@@ -0,0 +1,66 @@
+// Copyright 2012-2026 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Mirrors Go natsConnect helpers from test files.
+
+using NATS.Client.Core;
+using ZB.MOM.NatsNet.Server;
+
+namespace ZB.MOM.NatsNet.Server.IntegrationTests.Helpers;
+
+/// <summary>
+/// NATS.Client.Core wrapper helpers for integration test connections.
+/// Mirrors Go <c>natsConnect</c> pattern from test helper files.
+/// </summary>
+internal static class NatsTestClient
+{
+    // Default test connection options applied unless overridden.
+    private static readonly NatsOpts DefaultTestOpts = new()
+    {
+        Name           = "test-client",
+        ConnectTimeout = TimeSpan.FromSeconds(5),
+        RequestTimeout = TimeSpan.FromSeconds(10),
+    };
+
+    /// <summary>
+    /// Creates a <see cref="NatsConnection"/> to the given <paramref name="url"/> with
+    /// sensible test defaults. Settings in <paramref name="opts"/> override the defaults.
+    /// </summary>
+    public static NatsConnection Connect(string url, NatsOpts? opts = null)
+    {
+        var effective = opts ?? DefaultTestOpts;
+
+        // Always override the URL; apply default name when not supplied.
+        effective = effective with { Url = url };
+        if (string.IsNullOrEmpty(effective.Name))
+            effective = effective with { Name = DefaultTestOpts.Name };
+
+        return new NatsConnection(effective);
+    }
+
+    /// <summary>
+    /// Creates a <see cref="NatsConnection"/> to the given <paramref name="server"/>.
+    /// The URL is derived from the server's client port — uses the value from
+    /// <see cref="ServerOptions.Port"/> (resolved during server setup). When the server
+    /// was configured with port -1 (random), the actual port is stored in
+    /// <see cref="ServerOptions.Port"/> after Start().
+    /// </summary>
+    public static NatsConnection ConnectToServer(NatsServer server, NatsOpts? opts = null)
+    {
+        var port = server.Options.Port;
+        // Fallback to well-known port if options still show 0 or -1.
+        if (port <= 0) port = 4222;
+
+        return Connect($"nats://127.0.0.1:{port}", opts);
+    }
+}