Improve progress reporting (#145)

* Improve progress reporting

- Enable injecting an `IProgress<>` into a tool call to report progress when the client has supplied a progress token
- Add a custom type for ProgressToken and ProgressNotification to map to the schema
- Simplify RequestId to match ProgressToken's shape
- Serialize StdioClientTransport's SendMessageAsync implementation
- Add strongly-typed names for all request methods
- Change all request IDs created by McpJsonRpcEndpoint to include a guid for that endpoint

* Address PR feedback

src/ModelContextProtocol/Protocol/Types/RequestParamsMetadata.cs

@@ -1,3 +1,4 @@
+using ModelContextProtocol.Protocol.Messages;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol.Types;
@@ -11,5 +12,5 @@ public class RequestParamsMetadata
     /// If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
     /// </summary>
     [JsonPropertyName("progressToken")]
-    public object ProgressToken { get; set; } = default!;
+    public ProgressToken? ProgressToken { get; set; } = default!;
 }