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/NopProgress.cs

@@ -0,0 +1,12 @@
+namespace ModelContextProtocol;
+
+/// <summary>Provides an <see cref="IProgress{ProgressNotificationValue}"/> that's a nop.</summary>
+internal sealed class NullProgress : IProgress<ProgressNotificationValue>
+{
+    public static NullProgress Instance { get; } = new();
+
+    /// <inheritdoc />
+    public void Report(ProgressNotificationValue value)
+    {
+    }
+}