remainingPaintExtent property Null safety
The number of pixels of content that the sliver should consider providing. (Providing more pixels than this is inefficient.)
The actual number of pixels provided should be specified in the RenderSliver.geometry as SliverGeometry.paintExtent.
This value may be infinite, for example if the viewport is an unconstrained RenderShrinkWrappingViewport.
This value may be 0.0, for example if the sliver is scrolled off the bottom of a downwards vertical viewport.
final double remainingPaintExtent;