Instead of caching privs only for the current tick, and only for
NodeCore itself, change the base API to use caching universally,
including for naive mod code. Privs are cached until invalidated
by a change; it's assumed here that the "auth_reload" command
exists in the first place because this kind of caching is allowed
and accounted for, even if it's not actually done by the engine
or builtin.
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