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/asset_cache/iconforge/universal_icon.dm

@@ -487,7 +487,7 @@
 					var/dir_count = state_data["dirs"]
 					if(dir_count == 1)
 						base_icon_dir = SOUTH
-			else if(!length(icon_states(icon(curicon, curstate, NORTH))))
+			else if(!length(icon_states_fast(icon(curicon, curstate, NORTH))))
 				base_icon_dir = SOUTH
 
 		var/list/icon_dimensions = get_icon_dimensions(curicon)