refactored groups, separators and delays

src/core/setup.typ

@@ -1,5 +1,6 @@
 #import "utils.typ": is-elmt, get-group-span
 #import "../participant.typ": _exists as par-exists, _par
+#import "draw/group.typ": render-end as grp-render-end
 
 #let flatten-group(elmts, i) = {
   let group = elmts.at(i)
@@ -9,6 +10,7 @@
     group.elmts +
     ((
       type: "grp-end",
+      draw: grp-render-end,
       start-i: i
     ),) +
     elmts.slice(i+1)