Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/TokenProgress.cs

@@ -0,0 +1,16 @@
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol;
+
+/// <summary>
+/// Provides an <see cref="IProgress{ProgressNotificationValue}"/> tied to a specific progress token and that will issue
+/// progress notifications on the supplied endpoint.
+/// </summary>
+internal sealed class TokenProgress(IMcpEndpoint endpoint, ProgressToken progressToken) : IProgress<ProgressNotificationValue>
+{
+    /// <inheritdoc />
+    public void Report(ProgressNotificationValue value)
+    {
+        _ = endpoint.NotifyProgressAsync(progressToken, value, CancellationToken.None);
+    }
+}