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/Messages/RequestMethods.cs

@@ -0,0 +1,82 @@
+namespace ModelContextProtocol.Protocol.Messages;
+
+/// <summary>
+/// Provides names for request methods used in the Model Context Protocol (MCP).
+/// </summary>
+public static class RequestMethods
+{
+    /// <summary>
+    /// Sent from the client to request a list of tools the server has.
+    /// </summary>
+    public const string ToolsList = "tools/list";
+
+    /// <summary>
+    /// Used by the client to invoke a tool provided by the server.
+    /// </summary>
+    public const string ToolsCall = "tools/call";
+
+    /// <summary>
+    /// Sent from the client to request a list of prompts and prompt templates the server has.
+    /// </summary>
+    public const string PromptsList = "prompts/list";
+
+    /// <summary>
+    /// Used by the client to get a prompt provided by the server.
+    /// </summary>
+    public const string PromptsGet = "prompts/get";
+
+    /// <summary>
+    /// Sent from the client to request a list of resources the server has.
+    /// </summary>
+    public const string ResourcesList = "resources/list";
+
+    /// <summary>
+    /// Sent from the client to the server, to read a specific resource URI.
+    /// </summary>
+    public const string ResourcesRead = "resources/read";
+
+    /// <summary>
+    /// Sent from the client to request a list of resource templates the server has.
+    /// </summary>
+    public const string ResourcesTemplatesList = "resources/templates/list";
+
+    /// <summary>
+    /// Sent from the client to request resources/updated notifications from the server whenever a particular resource changes.
+    /// </summary>
+    public const string ResourcesSubscribe = "resources/subscribe";
+
+    /// <summary>
+    /// Sent from the client to request cancellation of resources/updated notifications from the server.
+    /// </summary>
+    public const string ResourcesUnsubscribe = "resources/unsubscribe";
+
+    /// <summary>
+    /// Sent from the server to request a list of root URIs from the client.
+    /// </summary>
+    public const string RootsList = "roots/list";
+
+    /// <summary>
+    /// A ping, issued by either the server or the client, to check that the other party is still alive.
+    /// </summary>
+    public const string Ping = "ping";
+
+    /// <summary>
+    /// A request from the client to the server, to enable or adjust logging.
+    /// </summary>
+    public const string LoggingSetLevel = "logging/setLevel";
+
+    /// <summary>
+    /// A request from the client to the server, to ask for completion options.
+    /// </summary>
+    public const string CompletionComplete = "completion/complete";
+
+    /// <summary>
+    /// A request from the server to sample an LLM via the client.
+    /// </summary>
+    public const string SamplingCreateMessage = "sampling/createMessage";
+
+    /// <summary>
+    /// This request is sent from the client to the server when it first connects, asking it to begin initialization.
+    /// </summary>
+    public const string Initialize = "initialize";
+}