HSS IPT persistence - preparatory work
This contains a mixed bag of prep work. It's the prefix of a WIP branch I have for IPT persistence.
Most of this is just shuffling about. The one piece of significant meat is "tor-hsservice: ipt_set: Change last_descriptor_expiry_including_slop". That's needed so that a loaded-from-disk PublishIptSet
can represent the previously-published IPTs, without having to entangle that with the IPT manager. The IPT manager will reconcile the information during its own startup. (That reconciliation during loading isn't in this branch yet, but it's in my WIP branch.)
Possibly @gabi-250 should take review since this overlaps with her publisher code.