Adds a unit test to detect double stacked lights (#73650)

## About The Pull Request

They make me sad and we should test for them
I use dir here to prevent like, bulb + bar stuff, idk if that's wanted
or not tho

_maps/map_files/Deltastation/DeltaStation2.dmm

@@ -30587,7 +30587,6 @@
 	},
 /area/station/science/auxlab/firing_range)
 "hrY" = (
-/obj/machinery/light/directional/north,
 /obj/item/flashlight/lamp,
 /obj/machinery/airalarm/directional/east,
 /obj/structure/table/wood,
@@ -43137,7 +43136,6 @@
 /turf/open/space/basic,
 /area/station/solars/port/aft)
 "kur" = (
-/obj/machinery/light/directional/south,
 /obj/item/kirbyplants/random,
 /obj/effect/turf_decal/tile/brown/half/contrasted,
 /obj/machinery/light/directional/south,

_maps/map_files/MetaStation/MetaStation.dmm

@@ -47655,7 +47655,6 @@
 "qUm" = (
 /obj/effect/spawner/random/vending/snackvend,
 /obj/machinery/light/directional/east,
-/obj/machinery/light/directional/east,
 /obj/structure/disposalpipe/segment{
 	dir = 9
 	},

code/modules/power/lighting/light.dm

@@ -88,6 +88,17 @@
 /obj/machinery/light/Initialize(mapload)
 	. = ..()
 
+	// Detect and scream about double stacked lights
+	if(PERFORM_ALL_TESTS(focus_only/stacked_lights))
+		var/turf/our_location = get_turf(src)
+		for(var/obj/machinery/light/on_turf in our_location)
+			if(on_turf == src)
+				continue
+			if(on_turf.dir != dir)
+				continue
+			stack_trace("Conflicting double stacked light [on_turf.type] found at ([our_location.x],[our_location.y],[our_location.z])")
+			qdel(on_turf)
+
 	if(!mapload) //sync up nightshift lighting for player made lights
 		var/area/our_area = get_room_area(src)
 		var/obj/machinery/power/apc/temp_apc = our_area.apc

code/modules/unit_tests/focus_only_tests.dm

@@ -26,3 +26,6 @@
 
 /// Checks that nightvision eyes have a full set of color lists
 /datum/unit_test/focus_only/nightvision_color_cutoffs
+
+/// Checks that no light shares a tile/pixel offsets with another
+/datum/unit_test/focus_only/stacked_lights