[Server] (Re-)Implement missing Notification & Request Handlers

For kicking off this SDK we used the Noticiation and Request handlers shipped with the Symfony MCP SDK and adopted schema component and registry.
But the MCP schema supports way more requests and notifications, that would need handlers as well. On php-mcp side this was the responsibility of the Dispatcher implementation.

Still open are:

• ListResourceTemplatesRequest
  #89
• ResourceSubscribeRequest
  #220
• ResourceUnsubscribeRequest
  #220
• SetLogLevelRequest
• CompletionCompleteRequest
  #97
• CancelledNotification

And potentially other requests and notification of the protocol.

Please announce yourself and create corresponding sub-issues before working on a specific handler - so we can avoid duplicate effort.

首先检查 src/Server/NotificationHandler 和 src/Server/RequestHandler 下现有的处理器，然后将其覆盖范围与 Symfony MCP SDK 和 php-mcp's Dispatcher.php 进行比较。该 issue 指出 SetLogLevelRequest 和 CancelledNotification 仍未完成，但协议中可能还存在其他缺口。对于缺失的协议请求和通知，达成相应的子 issue 以及处理器方案后，即视为完成。