title: Equivalent of the cacheExtent property for SliverChildBuilderDelegate
body: <p>I am trying to make a <code>CustomScrollView</code> that contains a <code>SliverList</code> in flutter. Since I want to build items in this list lazily, I have used the <code>SliverChildBuilderDelegate</code> as the delegate to <code>SliverList</code>. I was wondering whether there is any way I can change the size of the area that is drawn before being in the visible area?</p>
  <p>I am looking for an equivalent to the <a href="https://api.flutter.dev/flutter/widgets/ScrollView/cacheExtent.html" rel="nofollow noreferrer">cacheExtent</a> property.</p>