Adds the parcel cart to operations. (#21288)

This adds a parcel cart to the mail room in operations, which can be
loaded with up to 17 packages. These packages can be any that can be
held in the hand, so not crates but anything smaller effectively yes as
long as it can be wrapped in package wrapper.
When it is loaded with 5 packages, it gives a slowdown to the person
pushing it, and further slowdown at 11 packages.
The cart can have a total of 17 packages at the moment, as that is the
amount of different sprites I have for it.
The code is based on the engineering cart, and also contain a small
bugfix so the engineering cart give back steel when taken apart, as that
is what is used to build it.


https://github.com/user-attachments/assets/b8613c9e-55e1-4f76-926a-60f4acd6269e

### Asset Licenses
The following assets that **have not** been created by myself are
included in this PR:

| Path | Original Author | License |
| --- | --- | --- |
| icons/obj/parcelcart.dmi | Tomixcomics (Aurora Station) | CC-BY |

code/modules/modular_computers/file_system/programs/civilian/janitor.dm

@@ -48,8 +48,8 @@
 			var/mob/living/bot/cleanbot/C = A
 			status = C.on ? "Online" : "Offline"
 			supply_type = "Cleanbots"
-		else if(istype(A, /obj/structure/janitorialcart))
-			var/obj/structure/janitorialcart/J = A
+		else if(istype(A, /obj/structure/cart/storage/janitorialcart))
+			var/obj/structure/cart/storage/janitorialcart/J = A
 			status = J.get_short_status()
 			supply_type = "Janicarts"
 		else