* there's no need to pre-load follow requests for many users, since
at most we'll pack them for only 1 user (the one requesting the
data)
* similarly, it makes sense to preload security keys for many users
if we're serving a moderator's request, but if not, we need at most 1
user's keys (the requesting user's), and we can let `.pack()` fetch
those
* we always need to preload relations when serving a detailed
request, not only when the set of users to pack does not include the
requesting user
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