Enable netfx testing. (#588)

* Enable netfx testing.

* Skip impacted tests and re-enable netfx testing.

* Remove redundant comment.

* Remove unnecessary project configuration.

* Simplify test server copying.

src/Common/Polyfills/System/IO/StreamExtensions.cs

@@ -1,6 +1,7 @@
 using ModelContextProtocol;
 using System.Buffers;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace System.IO;
 
@@ -33,4 +34,31 @@ internal static class StreamExtensions
             }
         }
     }
+
+    public static ValueTask<int> ReadAsync(this Stream stream, Memory<byte> buffer, CancellationToken cancellationToken)
+    {
+        Throw.IfNull(stream);
+        if (MemoryMarshal.TryGetArray(buffer, out ArraySegment<byte> segment))
+        {
+            return new ValueTask<int>(stream.ReadAsync(segment.Array, segment.Offset, segment.Count, cancellationToken));
+        }
+        else
+        {
+            return ReadAsyncCore(stream, buffer, cancellationToken);
+            static async ValueTask<int> ReadAsyncCore(Stream stream, Memory<byte> buffer, CancellationToken cancellationToken)
+            {
+                byte[] array = ArrayPool<byte>.Shared.Rent(buffer.Length);
+                try
+                {
+                    int bytesRead = await stream.ReadAsync(array, 0, buffer.Length, cancellationToken).ConfigureAwait(false);
+                    array.AsSpan(0, bytesRead).CopyTo(buffer.Span);
+                    return bytesRead;
+                }
+                finally
+                {
+                    ArrayPool<byte>.Shared.Return(array);
+                }
+            }
+        }
+    }
 }

src/Common/Polyfills/System/IO/TextReaderExtensions.cs

@@ -1,10 +0,0 @@
-namespace System.IO;
-
-internal static class TextReaderExtensions
-{
-    public static Task<string> ReadLineAsync(this TextReader reader, CancellationToken cancellationToken)
-    {
-        cancellationToken.ThrowIfCancellationRequested();
-        return reader.ReadLineAsync();
-    }
-}