[keyserver] Use Set as an argument of fetchEntryInfosByID

Summary:
Refactor fetchEntryInfosByID so that it accepts a set of ids. Something similar could be done for fetchKnownUserInfos but it is used in a lot of places so it would be expensive.
Also, replace ids arrays with sets in checkState - that makes sense on its own, but also is beneficial because it makes interfaces of specs more unified.

https://linear.app/comm/issue/ENG-4654/unify-interfaces-in-session-utils

Test Plan:
Change some entries and users in the keyserver db, increase state check frequency, start the app and check if the state got fixed.
Add console logs in fetchEntryInfosByID and check if the correct result is returned.
Check if correct data is fetched in checkState.

Reviewers: kamil, bartek, inka

Reviewed By: kamil, bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8925