New boxes (#21439)

* Thoroughly resprites boxes. They're now more modular and, importantly,
colorable.
* Resprites cardboard, as a material.
* Repaths boxes behind the scenes to be more object-oriented, with boxes
being resorted into their own subtypes. You might notice this in the
gargantuan amount of files this PR changes.

Part of a bigger (yet modestly-sized still) resprites project. Atomized
the boxes bit into this PR specifically so that any conflicts don't
destroy any other spriting PRs.

<img width="652" height="273" alt="image"
src="https://github.com/user-attachments/assets/5590b22d-c9d7-49b5-9adf-0b6e01a6962b"
/>

<img width="383" height="345" alt="image"
src="https://github.com/user-attachments/assets/aab83040-2d5d-4283-b019-3d6bed2e3e47"
/>

<img width="142" height="343" alt="image"
src="https://github.com/user-attachments/assets/75a98d36-0171-4e48-9dec-de5511f35d39"
/>

<img width="127" height="225" alt="image"
src="https://github.com/user-attachments/assets/a1ff8b1b-bd2a-4c0d-b538-32fe401724c3"
/>

<img width="334" height="399" alt="image"
src="https://github.com/user-attachments/assets/e41330ac-ed4a-4e81-a87a-5ba901b47b5c"
/>

code/game/objects/random/weapon.dm

@@ -36,10 +36,10 @@
 	icon = 'icons/obj/ammo.dmi'
 	icon_state = "45-10"
 	problist = list(
-		/obj/item/storage/box/beanbags = 6,
-		/obj/item/storage/box/shotgunammo = 2,
-		/obj/item/storage/box/shotgunshells = 4,
-		/obj/item/storage/box/stunshells = 1,
+		/obj/item/storage/box/shells/beanbags = 6,
+		/obj/item/storage/box/shells/slugs = 2,
+		/obj/item/storage/box/shells/buckshot = 4,
+		/obj/item/storage/box/shells/stunshells = 1,
 		/obj/item/ammo_magazine/c45m = 2,
 		/obj/item/ammo_magazine/c45m/rubber = 4,
 		/obj/item/ammo_magazine/c45m/flash = 4,