smb: implement kdirnotify support

to track file changes/add/removals for smb:// uris

since smbclient isn't properly thread safe right now, we use separate processes per URI to notify on changes

a kded module listens to kdirnotify dir enter events and spawns a notifier subprocess. the notifier then attempts to open a notify loop with the remote. authentication ought to be handled via the kiod auth cache, that is to say: when cached auth isn't available or not valid the notifier will simply not work at all. there's no interactive auth queries as they'd lack context from a KIO pov

depends on smb-auth refactor