Ore vents now turn transparent and clickthrough when there's a mob behind them (#95646)

## About The Pull Request

When a mob enters a tile above the vent its top half (and the rig, if
the vent has been tapped) will turn transparent and clickthrough. The
bottom half residing on the tile below is still clickable.


https://github.com/user-attachments/assets/5ed1cd3a-4f33-4692-adce-471eb2942d45

Same applies to ore type overlays. Also I've cleaned up ore vent code a
bit.

## Why It's Good For The Game

During combat some mobs, especially legion skulls, can end up hiding
behind the vent and be extremely hard to hit, requiring the player to
pull up the alt click menu to dispatch of them. This should resolve that
issue.

## Changelog
🆑
qol: Ore vents now turn transparent and clickthrough when a mob enters
the tile above them. The bottom half of the vent is still clickable.
code: Cleaned up ore vent code
/🆑

code/modules/mining/equipment/mineral_scanner.dm

@@ -113,7 +113,7 @@
 	layer = FLASH_LAYER
 	icon = 'icons/effects/ore_visuals.dmi'
 	appearance_flags = NONE // to avoid having TILE_BOUND in the flags, so that the 480x480 icon states let you see it no matter where you are
-	duration = 35
+	duration = 3.5 SECONDS
 	pixel_x = -224
 	pixel_y = -224
 	/// What animation easing to use when we create the ore overlay on rock walls/ore vents.
@@ -122,11 +122,3 @@
 /obj/effect/temp_visual/mining_overlay/Initialize(mapload)
 	. = ..()
 	animate(src, alpha = 0, time = duration, easing = easing_style)
-
-/obj/effect/temp_visual/mining_overlay/vent
-	icon = 'icons/effects/vent_overlays.dmi'
-	icon_state = "unknown"
-	duration = 45
-	pixel_x = 0
-	pixel_y = 0
-	easing_style = CIRCULAR_EASING|EASE_IN