[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.

Comienza revisando los handlers existentes en src/Server/NotificationHandler y src/Server/RequestHandler; después, compara su cobertura con Symfony MCP SDK y php-mcp's Dispatcher.php. El issue identifica SetLogLevelRequest y CancelledNotification como aún pendientes, aunque pueden quedar otras carencias del protocolo. Se considera terminado cuando se hayan acordado los sub-issues y los handlers correspondientes para las solicitudes y notificaciones del protocolo que falten.