Misc. Optimizations (#3993)

changes:

Overlays now creates less temporary lists.
Falling no longer queues unsimulated atoms that wouldn't fall anyways (incl. LOs).
Pixel-shifted AO is now cached too.
Changed some references to get_map_cell() to macro equivalents in random maps.
Added smoothing hinting to the icon smoother, allowing for major performance improvements in common cases.
Space initialization no longer involves appearance churn (and is much faster as a result).

code/modules/mining/mine_turfs.dm

@@ -15,13 +15,15 @@
 	gender = PLURAL
 	var/icon/actual_icon = 'icons/turf/smooth/rock_wall.dmi'
 	layer = 2.01
-	smooth = SMOOTH_MORE | SMOOTH_BORDER
+	smooth = SMOOTH_MORE | SMOOTH_BORDER | SMOOTH_NO_CLEAR_ICON
+	smoothing_hints = SMOOTHHINT_CUT_ON_ALL_F | SMOOTHHINT_ONLY_MATCH_TURF | SMOOTHHINT_TARGETS_NOT_UNIQUE
 	canSmoothWith = list(
 		/turf/simulated/mineral,
 		/turf/simulated/wall,
 		/turf/unsimulated/wall,
 		/turf/simulated/shuttle
 	)
+
 	oxygen = 0
 	nitrogen = 0
 	opacity = 1
@@ -509,6 +511,7 @@
 	icon_state = "ash"
 	desc = "A fine grey ash. Looks pretty tightly packed."
 	smooth = SMOOTH_MORE | SMOOTH_BORDER | SMOOTH_NO_CLEAR_ICON
+	smoothing_hints = SMOOTHHINT_CUT_ON_ALL_F | SMOOTHHINT_ONLY_MATCH_TURF | SMOOTHHINT_TARGETS_NOT_UNIQUE
 	gender = PLURAL
 	canSmoothWith = list(
 		/turf/simulated/floor/asteroid,