Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol/Protocol/EmptyResult.cs

@@ -1,13 +0,0 @@
-using System.Text.Json.Serialization;
-
-namespace ModelContextProtocol.Protocol;
-
-/// <summary>
-/// Represents an empty result object for operations that need to indicate successful completion 
-/// but don't need to return any specific data.
-/// </summary>
-public class EmptyResult
-{
-    [JsonIgnore]
-    internal static EmptyResult Instance { get; } = new();
-}