Function build_clusters 

fn build_clusters(
    world: &mut World,
    context: RenderContext,
    pass: Entity,
    _ui: Option<Entity>,
    size: (u32, u32),
    _options: SceneOptions,
) -> SceneControl

Build the cluster debug scene’s world content.

One long floor, a handful of short-ranged lights and a fragment that overlays the grid on the lighting: nothing of the lit scene is reused, because what this scene has to show is where the counts differ, and the lit scene’s lights reach nearly every cell.