added auto fit wrapper function

src/diagram.typ

@@ -1,4 +1,4 @@
-#import "utils.typ": get-group-span
+#import "utils.typ": get-group-span, fit-canvas
 #import "renderer.typ": render
 #import "participant.typ" as participant: _par, PAR-SPECIALS
 
@@ -18,7 +18,7 @@
   ),)
 }
 
-#let diagram(elements) = {
+#let diagram(elements, width: auto) = {
   if elements == none {
     return
   }
@@ -188,7 +188,8 @@
   }
 
   set text(font: "Source Sans 3")
-  render(participants, elmts)
+  let canvas = render(participants, elmts)
+  fit-canvas(canvas, width: width)
 }
 
 #let from-plantuml(code) = {