Explosions severing cable networks cause nearby(ish) connected rooms's lights to flicker. Also reduces cable integrity. (#91263)

## About The Pull Request

- If a cable is destroyed by an explosion, all rooms within 64-100 (it's
a probability) tiles AND which are connected to the same powernet as the
split cable will have their lights flicker 1-3 times.

- Also adds a verb for visualizing powernets.

- Reduces cable integrity from 300 to 50.

- Cables have innate 75% bomb armor when under a floor tile.

## Why It's Good For The Game

- A big devastating explosion a few doors down is, usually, not felt at
all outside of the screen shake. This adds a bit more ambience to the
effect - you hear a big explosion, your screen goes wild, and the lights
cut for just a second.

- Verb just makes it easier to trace powernets.

- I found it a little ridiculous that cables have 300 integrity, the
same as most furniture. This ultimately makes them a lot more vulnerable
to stuff like acid and fire.

- To compensate for their drastically reduced integrity, I gave cables a
considerable boost to explosive resistance while concealed under the
floor. This prevents bombs from outright shredding all cables in a 50
mile radius. (Devastating explosions will still one-tap them, but heavy
explosions will on average take two blasts.)

## Changelog

🆑 Melbert
add: If a cable is destroyed by an explosion, all rooms within 64-100
(it's a probability) tiles AND which are connected to the same powernet
as the split cable will have their lights flicker 1-3 times.
balance: Cable integrity has been reduced from 300 to 50
balance: Cables have an innate 75% bomb resistance while under floor
tiles
/🆑

code/game/objects/effects/misc.dm

@@ -87,3 +87,7 @@
 /obj/effect/abstract/marker/intercom
 	name = "intercom range marker"
 	color = COLOR_YELLOW
+
+/obj/effect/abstract/marker/powernet
+	name = "powernet run marker"
+	var/powernet_owner