Elevates (almost all) inventory variables from /carbon to /human (#96955)

## About The Pull Request

Moves all inventory slots but handcuffs/legcuffs (as those can be used
by xenos) from ``/carbon`` onto ``/human``, as xenos do not use any of
those inventory slots, only leaving them in use by humans. Their
presence on ``/carbon`` is an artifact of times when monkeys weren't
humans, and some of the slots had to be shared by all carbons.
In some places I've used ``get_item_by_slot`` rather than swapping
checks to ``ishuman`` for simplicity's sake, in some places it might not
be the most optimal solution but in cases like help act any other
solution would require a refactor of the whole (massive) proc.

## Why It's Good For The Game

Cleaner/more sensible code, one step closer to fully datumized
inventories.

## Changelog
🆑
refactor: Moved a lot of human-specific inventory code onto human mobs,
report if inventories break!
/🆑

code/game/objects/items/devices/laserpointer.dm

@@ -237,7 +237,7 @@
 			//Intensity of the laser dot to pass to flash_act
 			var/severity = pick(0, 1, 2)
 			var/always_fail = FALSE
-			if(istype(target_humanoid.glasses, /obj/item/clothing/glasses/eyepatch) && prob(50))
+			if(istype(target_humanoid.get_item_by_slot(ITEM_SLOT_EYES), /obj/item/clothing/glasses/eyepatch) && prob(50))
 				always_fail = TRUE
 
 			//chance to actually hit the eyes depends on internal component

code/game/objects/items/devices/radio/electropack.dm

@@ -33,11 +33,9 @@
 
 //ATTACK HAND IGNORING PARENT RETURN VALUE
 /obj/item/electropack/attack_hand(mob/user, list/modifiers)
-	if(iscarbon(user))
-		var/mob/living/carbon/C = user
-		if(src == C.back)
-			to_chat(user, span_warning("You need help taking this off!"))
-			return
+	if(user.get_item_by_slot(ITEM_SLOT_BACK) == src)
+		to_chat(user, span_warning("You need help taking this off!"))
+		return
 	return ..()
 
 /obj/item/electropack/item_interaction(mob/living/user, obj/item/tool, list/modifiers)