Optimize cardboard cutouts saving 1.5s+ on init times (#73404)

New regression in init times. Closes
https://github.com/tgstation/dev-cycles-initiative/issues/32. CC @Fikou

- Instead of creating a human and icon for *every* cardboard cutout when
initialized, only creates the one we're actually using. When you're
about to use a crayon, creates all of them.
- Instead of using getFlatIcon, uses appearances directly.

code/modules/mapping/mapping_helpers.dm

@@ -387,8 +387,6 @@ INITIALIZE_IMMEDIATE(/obj/effect/mapping_helpers/no_lava)
 	var/l_hand = NO_REPLACE
 	/// Which slots on the mob should be bloody?
 	var/bloody_slots = NONE
-	/// Directions we generate for the mob.
-	var/generated_dirs = list(NORTH, SOUTH, EAST, WEST)
 	/// Do we draw more than one frame for the mob?
 	var/animated = TRUE
 
@@ -406,7 +404,7 @@ INITIALIZE_IMMEDIATE(/obj/effect/mapping_helpers/no_lava)
 	return TRUE
 
 /obj/effect/mapping_helpers/atom_injector/human_icon_injector/inject(atom/target)
-	apply_dynamic_human_icon(target, outfit_path, species_path, mob_spawn_path, r_hand, l_hand, bloody_slots, generated_dirs, animated)
+	apply_dynamic_human_appearance(target, outfit_path, species_path, mob_spawn_path, r_hand, l_hand, bloody_slots, animated)
 
 /obj/effect/mapping_helpers/atom_injector/human_icon_injector/generate_stack_trace()
 	. = ..()