Add notification support

Co-authored-by: Kevin Fischer <kfischer_okarin@yahoo.co.jp>

lib/mcp/server/transports/stdio_transport.rb

@@ -43,10 +43,18 @@ module MCP
           $stdout.flush
         end
 
-        def send_response(message)
-          json_message = message.is_a?(String) ? message : JSON.generate(message)
-          $stdout.puts(json_message)
-          $stdout.flush
+        def send_notification(method, params = nil)
+          notification = {
+            jsonrpc: "2.0",
+            method: method,
+          }
+          notification[:params] = params if params
+
+          send_response(notification)
+          true
+        rescue => e
+          MCP.configuration.exception_reporter.call(e, { error: "Failed to send notification" })
+          false
         end
       end
     end