Makes decals unhittable in combat mode, reduces vent debris spawns (#96859)

## About The Pull Request
Cleanable decals, such as rubble, trash, glass shards, etc, can no
longer be hit (not interacted with, but just offensively hit) in combat
mode.
Ore vents now more consistently clear rocks around them, and spawn
noticeably less debris.

## Why It's Good For The Game

Suggested under my necropolis tile PR, some larger decals may steal your
clicks in combat which I do not think offers any positive gameplay
value.
Ore vents just spawn too much debris, and as it only has one sprite, it
just looks really bad.

## Changelog
🆑
qol: Ore vents spawn less rubble and are more consistent at excavating
the surrounding area
balance: Cleanable decals can no longer be hit (not cleaned, just hit)
if the user has combat mode on.
/🆑

code/game/objects/items/devices/earthcracker.dm

@@ -151,15 +151,15 @@
 		for(var/turf/rock in oview(i)) // This collects a list of rings of turfs (in a growing radius of i) that we'll applying logic to "drill" below.
 
 			if(istype(rock, /turf/closed/mineral))
-				if(prob(50 + (i * 8)))
+				if(prob((i * 15) - 25))
 					continue
 				var/turf/closed/mineral/drillable = rock
 				drillable.gets_drilled(user)
-				if(prob(50))
+				if(prob(15))
 					new /obj/effect/decal/cleanable/rubble(rock)
 				continue
 
-			if(istype(rock, /turf/open/misc/asteroid) && prob(35))
+			if(istype(rock, /turf/open/misc/asteroid) && prob(10))
 				new /obj/effect/decal/cleanable/rubble(rock)
 				continue
 		sleep(0.6 SECONDS)