Only request data that isn't already present in the cache.
Overwrites a base connection's
getListData to use data in the cache
whenever possible. This works by getting the stored sets
from the cache and
doing a diff to see what needs to be loaded from the base
connection and what can be loaded from the cache.
With that information, this
getListData requests data from the cache or the base connection as needed.
Data loaded from different sources is combined via getUnion.
the parameters of the list that is being requested.