also mark the sync version as NeverAsync. a blocking wait on sqlite
locks in a coroutine may never finish if it's a different coroutine
on the same executor that is holding the lock, not another process.
this propagates to the sqlite core interface, but no further. we'll
assume that caches do not block on a database for very long, and we
can't reasonably propagate never-async-ness out of stores unless we
touch everything we'd touch for the async transition, again, twice.
store code already assumes that it can block for however long it'll
feel like that moment. we keep thread pools around for this reason.
Change-Id: I62f77e1ac333cbe2e4e646dbcb1571463f2cf3fc
eldritch horrors
044b4c4500