Add Preloading Feature

Suggestion from #14:

Add an option such as `preload: 30`, which would attempt to preload data for the next pages up to 30 documents in advance.

Start by reviewing issue #14 and locating the existing pagination and data-loading entry points; the payload names no files or tests. Define how an option such as `preload: 30` should behave, then verify that it attempts to load up to 30 documents from subsequent pages without changing normal pagination.

Written by the indexing model from the issue text.