move the internal preview to canvas (#18930)

* move the internal preview to canvas

* use a helper

* basic readme prep

* .

* .

* transform  better

* byond can't handle icon states of large files...

* move fully to the rust version

* fix typing

* just wtf. NO

* fix the legacy path

* keep it all centralized

* tiny oversight

* unit test rewrite

* rename

* fix bad layering

* fixes a bunch of layering issues

* artifact

* move crash to log_runtime

* missing overlay warning

* why not

code/modules/persistence/graffiti.dm

@@ -25,7 +25,7 @@
 		author = _author
 
 /obj/effect/decal/writing/Initialize(mapload)
-	var/list/random_icon_states = cached_icon_states(icon)
+	var/list/random_icon_states = icon_states_fast(icon)
 	for(var/obj/effect/decal/writing/writing in loc)
 		random_icon_states.Remove(writing.icon_state)
 	if(length(random_icon_states))