feat: implement resource update notifications (#264)

This enables servers to notify clients when specific resources are updated,
allowing clients to react to individual resource changes rather than just
list changes.

- Add ResourcesUpdatedNotification schema with uri field
- Add METHOD_NOTIFICATION_RESOURCES_UPDATED constant
- Implement notifyResourcesUpdated() methods in McpAsyncServer and McpSyncServer
- Add client-side support for resource update consumers and handlers
- Client automatically reads updated resource content when notification received
- Add tests for both async and sync server implementations

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>