test: add E2E WebSocket transport tests (connect, pub/sub round-trip)

tests/NATS.E2E.Tests/Infrastructure/WebSocketServerFixture.cs

@@ -0,0 +1,37 @@
+using NATS.Client.Core;
+
+namespace NATS.E2E.Tests.Infrastructure;
+
+public sealed class WebSocketServerFixture : IAsyncLifetime
+{
+    private NatsServerProcess _server = null!;
+
+    public int Port => _server.Port;
+    public int WsPort { get; private set; }
+
+    public async Task InitializeAsync()
+    {
+        WsPort = NatsServerProcess.AllocateFreePort();
+
+        var config = $$"""
+            websocket {
+                listen: 127.0.0.1:{{WsPort}}
+                no_tls: true
+            }
+            """;
+
+        _server = NatsServerProcess.WithConfig(config);
+        await _server.StartAsync();
+    }
+
+    public async Task DisposeAsync()
+    {
+        await _server.DisposeAsync();
+    }
+
+    public NatsConnection CreateNatsClient()
+        => new(new NatsOpts { Url = $"nats://127.0.0.1:{Port}" });
+}
+
+[CollectionDefinition("E2E-WebSocket")]
+public class WebSocketCollection : ICollectionFixture<WebSocketServerFixture>;