Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/Protocol/UnsubscribeRequestParams.cs

@@ -0,0 +1,27 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Sent from the client to cancel resource update notifications from the server for a specific resource.
+/// </summary>
+/// <remarks>
+/// <para>
+/// After a client has subscribed to resource updates using <see cref="SubscribeRequestParams"/>, 
+/// this message can be sent to stop receiving notifications for a specific resource. 
+/// This is useful for conserving resources and network bandwidth when 
+/// the client no longer needs to track changes to a particular resource.
+/// </para>
+/// <para>
+/// The unsubscribe operation is idempotent, meaning it can be called multiple times 
+/// for the same resource without causing errors, even if there is no active subscription.
+/// </para>
+/// </remarks>
+public class UnsubscribeRequestParams : RequestParams
+{
+    /// <summary>
+    /// The URI of the resource to unsubscribe from. The URI can use any protocol; it is up to the server how to interpret it.
+    /// </summary>
+    [JsonPropertyName("uri")]
+    public string? Uri { get; init; }
+}