iris: make span compaction explicit

examples/tabs/lib.rs

@@ -100,10 +100,12 @@ where
             rect(PaintId::PURPLE).sized((50, 50)).align(Align::TOP),
         )
             .span(Dir::RIGHT)
+            .compact()
             .center(),
         wtext("pretty cool right?").size(50),
     )
         .span(Dir::DOWN)
+        .compact()
         .add(rsc);
 
     let texts = Span::empty(Dir::DOWN).gap(10).add(rsc);