refactored sequences, sync and gaps

src/diagram.typ

@@ -1,13 +1,19 @@
-#import "core/utils.typ": fit-canvas
+#import "core/utils.typ": fit-canvas, set-ctx
 #import "core/renderer.typ": render
 #import "participant.typ" as participant: _par, PAR-SPECIALS
 #import "sequence.typ": _seq
-
+#import "core/draw/event.typ": render as evt-render
 #import "core/setup.typ": setup
 
+#let gap-render(gap) = set-ctx(ctx => {
+  ctx.y -= gap.size
+  return ctx
+})
+
 #let _gap(size: 20) = {
   return ((
     type: "gap",
+    draw: gap-render,
     size: size
   ),)
 }
@@ -15,6 +21,7 @@
 #let _evt(participant, event) = {
   return ((
     type: "evt",
+    draw: evt-render,
     participant: participant,
     event: event,
     lifeline-style: auto