The callers either set a default limit or manually handle a None-limit
later on (by setting a default value).
Update the callers to always instantiate PaginationConfig with a default
limit and then assume the limit is non-None.
This makes the serialization of events synchronous (and it no
longer access the database), but we must manually calculate and
provide the bundled aggregations.
Overall this should cause no change in behavior, but is prep work
for other improvements.
