Add target check for public account targeted notes

For the notes which target public accounts we should add an explicit check inside the builder that the target is indeed public.

This includes at least `RbacActionNote` and `OwnerActionNote`, but we should double check whether there are other ones.

_Originally posted by @PhilippGackstatter in https://github.com/0xMiden/protocol/pull/3274#discussion_r3578777392_