Refactor transports to help enable graceful shutdown (#142)

- This also paves the way for better multi-session support
- We should definitely rethink names for the transport API
- For now, I kept the names similar as possible, so we can
  focus on the API shape

Co-authored-by: Stephen Toub <stoub@microsoft.com>

tests/ModelContextProtocol.Tests/Utils/LoggedTest.cs

@@ -3,16 +3,27 @@ using ModelContextProtocol.Test.Utils;
 
 namespace ModelContextProtocol.Tests.Utils;
 
-public class LoggedTest(ITestOutputHelper testOutputHelper)
+public class LoggedTest : IDisposable
 {
-    public ITestOutputHelper TestOutputHelper { get; } = testOutputHelper;
-    public ILoggerFactory LoggerFactory { get; } = CreateLoggerFactory(testOutputHelper);
+    private readonly DelegatingTestOutputHelper _delegatingTestOutputHelper;
 
-    private static ILoggerFactory CreateLoggerFactory(ITestOutputHelper testOutputHelper)
+    public LoggedTest(ITestOutputHelper testOutputHelper)
     {
-        return Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        _delegatingTestOutputHelper = new()
         {
-            builder.AddProvider(new XunitLoggerProvider(testOutputHelper));
+            CurrentTestOutputHelper = testOutputHelper,
+        };
+        LoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        {
+            builder.AddProvider(new XunitLoggerProvider(_delegatingTestOutputHelper));
         });
     }
+
+    public ITestOutputHelper TestOutputHelper => _delegatingTestOutputHelper;
+    public ILoggerFactory LoggerFactory { get; }
+
+    public virtual void Dispose()
+    {
+        _delegatingTestOutputHelper.CurrentTestOutputHelper = null;
+    }
 }