Use Kestrel for all in-memory HTTP tests (#225)

* Add route pattern parameter to MapMcp
* Add configureOptionsAsync
* Use Kestrel for all in-memory HTTP tests
* Use ApplicationStopping token for SSE responses
* Use RegisterNotificationHandler in MapMcp tests
* Work around SocketsHttpHandler bug where it doesn't call DispseAsync on the stream returned by the ConnectCallback

tests/ModelContextProtocol.Tests/Transport/SseResponseStreamTransportTests.cs

@@ -0,0 +1,27 @@
+using ModelContextProtocol.Protocol.Transport;
+using ModelContextProtocol.Tests.Utils;
+using System.IO.Pipelines;
+
+namespace ModelContextProtocol.Tests.Transport;
+
+public class SseResponseStreamTransportTests(ITestOutputHelper testOutputHelper) : LoggedTest(testOutputHelper)
+{
+    [Fact]
+    public async Task Can_Customize_MessageEndpoint()
+    {
+        var responsePipe = new Pipe();
+
+        await using var transport = new SseResponseStreamTransport(responsePipe.Writer.AsStream(), "/my-message-endpoint");
+        var transportRunTask = transport.RunAsync(TestContext.Current.CancellationToken);
+
+        using var responseStreamReader = new StreamReader(responsePipe.Reader.AsStream());
+        var firstLine = await responseStreamReader.ReadLineAsync(TestContext.Current.CancellationToken);
+        Assert.Equal("event: endpoint", firstLine);
+
+        var secondLine = await responseStreamReader.ReadLineAsync(TestContext.Current.CancellationToken);
+        Assert.Equal("data: /my-message-endpoint", secondLine);
+
+        responsePipe.Reader.Complete();
+        responsePipe.Writer.Complete();
+    }
+}