Refactor round start volume of welding packs and fryers (#23027)

# Summary

This PR adjust welding packs and fryers. Welding packs now spawn empty
[on the Horizon] to encourage the persistent welding tanks and fryers
have their optimal oil level adjusted to balance out oil refills.

**Depends on https://github.com/Aurorastation/Aurora.3/pull/23005**.

## Changes

- Added new sprite for empty welding packs.
(Regular vs new low variant)
<img width="835" height="108" alt="image"
src="https://github.com/user-attachments/assets/a882bff1-901b-4b0e-8d1d-750ed4e1e83c"
/>

- Welding packs now spawn empty (only on the Horizon and during map
load).
- Deep fryer no longer contain 9 full tanks of cooking oil. They contain
100u now and make refills using the [persistent cooking oil
tanks](https://github.com/Aurorastation/Aurora.3/pull/23005) much more
reasonable. Added a wrench to the kitchen for tank handling.

code/modules/reagents/reagent_containers/welding_backpack.dm

@@ -15,6 +15,16 @@
 	drop_sound = 'sound/items/drop/backpack.ogg'
 	pickup_sound = 'sound/items/pickup/backpack.ogg'
 
+/obj/item/reagent_containers/weldpack/Initialize(mapload)
+	var/turf/T = get_turf(src)
+	if(mapload && T && is_station_level(T.z))
+		// If the weldpack is spawned on a station level during map load, don't give it any fuel.
+		// This is in support of persistent welding fuel tanks and only for the persistent levels.
+		reagents_to_add = null
+		create_reagents(volume) // Ensure reagents datum is created, even if empty
+		update_volume()
+	. = ..() // After reagents_to_add is updated
+
 /obj/item/reagent_containers/weldpack/feedback_hints(mob/user, distance, is_adjacent)
 	. += ..()
 	if(ishuman(loc) && user != loc) // what if we want to sneak some reagents out of somewhere?
@@ -27,6 +37,20 @@
 	else
 		. += SPAN_WARNING("\The [src] is empty!")
 
+/obj/item/reagent_containers/weldpack/proc/update_volume()
+	var/fill_level = reagents.total_volume / volume
+	if(fill_level <= 0.1)
+		icon_state = "welderpack_low"
+		item_state = "welderpack_low"
+	else
+		icon_state = "welderpack"
+		item_state = "welderpack"
+	update_icon()
+	update_worn_icon()
+
+/obj/item/reagent_containers/weldpack/on_reagent_change()
+	update_volume()
+
 /obj/item/reagent_containers/weldpack/attackby(obj/item/attacking_item, mob/user)
 	if(attacking_item.tool_behaviour == TOOL_WRENCH)
 		if(atom_flags & ATOM_FLAG_OPEN_CONTAINER)
@@ -60,5 +84,6 @@
 			reagents.trans_type_to(attacking_item, /singleton/reagent/fuel, min(fuel_volume, T.reagents.maximum_volume - tool_fuel_volume))
 			to_chat(user, SPAN_NOTICE("Welder refilled!"))
 			playsound(loc, 'sound/effects/refill.ogg', 50, 1, -6)
+			update_volume()
 		return
 	return ..()