Adds Climbing to a Bunch of Old Stuff (#81283)

## About The Pull Request

What it says. a lot of old atmospherics stuff and a few other
unintuitive things lacked climbability sometimes leading to stupid
situations where you could get stuck or their use as inappropriate
obstacles.

Canisters, pumps/scrubbers, welding/water/foam tanks, heaters, and racks
can now be climbed.


![image](https://github.com/tgstation/tgstation/assets/3894717/1e5582c5-8b41-42c6-99e8-810970adc1e9)

![image](https://github.com/tgstation/tgstation/assets/3894717/78c31589-1088-4e25-8194-d27316e526e2)

![image](https://github.com/tgstation/tgstation/assets/3894717/bc7625a5-6d0f-4b4a-adb3-a52e9eb8d04b)


## Why It's Good For The Game

i remember when tables were a kit you could carry, immediately assemble,
and then use to two-click table somebody to kill them. somehow this
seems overdue.

## Changelog

🆑
qol: portable air pumps, scrubbers, heaters, canisters, liquid tanks,
and racks are now climbable.
/🆑

code/game/objects/structures/tables_racks.dm

@@ -825,6 +825,11 @@
 	pass_flags_self = LETPASSTHROW //You can throw objects over this, despite it's density.
 	max_integrity = 20
 
+/obj/structure/rack/Initialize(mapload)
+	. = ..()
+	AddElement(/datum/element/climbable)
+	AddElement(/datum/element/elevation, pixel_shift = 12)
+
 /obj/structure/rack/examine(mob/user)
 	. = ..()
 	. += span_notice("It's held together by a couple of <b>bolts</b>.")