Forearm crutches + Pair of crutches in loadout (#20863)

Adds a forearm crutch to the game, as well as the ability to select a
pair of crutches in the loadout.
The sprites for it are made by Plyushsune, and altered by me.

code/game/objects/items/weapons/storage/boxes.dm

@@ -1485,3 +1485,13 @@
 	starts_with = list(
 		/obj/item/reagent_containers/food/drinks/bottle/small/burukutu = 6
 	)
+
+/obj/item/storage/box/crutch_pair
+	starts_with = list(
+		/obj/item/cane/crutch = 2
+	)
+
+/obj/item/storage/box/forearm_crutch_pair
+	starts_with = list(
+		/obj/item/cane/crutch/forearm = 2
+	)