base for CeTZ integration

migrated contextual variables to CeTZ context shared-state
adapted participant rendering

src/core/utils.typ

@@ -1,3 +1,5 @@
+#import "../cetz.typ": draw
+
 #let is-elmt(elmt) = {
   if type(elmt) != dictionary {
     return false
@@ -89,4 +91,16 @@
     height: new-h,
     scale(x: r, y: r, reflow: true, canvas)
   )
+})
+
+#let set-ctx(func) = draw.set-ctx(c => {
+  let ctx = c.shared-state.chronos
+  ctx = func(ctx)
+  c.shared-state.chronos = ctx
+  return c
+})
+
+#let get-ctx(func) = draw.get-ctx(c => {
+  let ctx = c.shared-state.chronos
+  func(ctx)
 })