Function cull_offscreen 

pub fn cull_offscreen(
    commands: Commands<'_, '_>,
    viewport: Res<'_, Viewport>,
    rects: Query<'_, '_, (Entity, &ExtractedRect)>,
    texts: Query<'_, '_, (Entity, &ExtractedText)>,
)

Despawns extracted entities whose AABB lies fully outside the Viewport.

• Runs in RenderStage::Prepare (registered automatically by App::new).
• Performs only an AABB test against the viewport; partial-overlap clipping is the renderer’s responsibility.