Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/NopProgress.cs

@@ -0,0 +1,19 @@
+namespace ModelContextProtocol;
+
+/// <summary>Provides an <see cref="IProgress{ProgressNotificationValue}"/> that's a nop.</summary>
+internal sealed class NullProgress : IProgress<ProgressNotificationValue>
+{
+    /// <summary>
+    /// Gets the singleton instance of the <see cref="NullProgress"/> class that performs no operations when progress is reported.
+    /// </summary>
+    /// <remarks>
+    /// Use this property when you need to provide an <see cref="IProgress{T}"/> implementation 
+    /// but don't need to track or report actual progress.
+    /// </remarks>
+    public static NullProgress Instance { get; } = new();
+
+    /// <inheritdoc />
+    public void Report(ProgressNotificationValue value)
+    {
+    }
+}