We make LoginAction a simple wrapper around processing the unknown
action to expose too much internal logic. This allows us to have a
must_use on our LoginAction type, otherwise the SingleUnkIdAction's
must_use will be lost when returned in the login action.
Fixes: a5cdddbb2b ("user can upgrade their npub -> nsec")
Signed-off-by: William Casarin <jb55@jb55.com>