Fix ammo pile scatter crash (#23062)

* Please describe the intent of your changes in a clear fashion.
Addresses a "list index out of bounds" error occurring in
`obj/item/ammo_pile/proc/remove_ammo` when
`obj/item/ammo_pile/proc/scatter()` was called.

The root cause was a race condition where `scatter()` iterated over the
`ammo` list and called `remove_ammo()` for each item. `remove_ammo()` in
turn called `check_ammo()`, which would `qdel(src)` (and thus empty the
`ammo` list) when only one round remained. This left `scatter()` to
continue its loop and call `remove_ammo()` on an already empty list,
leading to the crash.

The fix rewrites `scatter()` to directly handle the unregistering of
signals, force-moving, and throwing of each bullet. After all bullets
have been processed, the `ammo` list is cleared, overlays are cut, and
the pile is `qdel`'d. This avoids the problematic mid-loop calls to
`remove_ammo()` and `check_ammo()`, preventing the list index out of
bounds error.
* Please make sure that, in the case of mapping changes, you include
images of these changes in the PR's description.
* Please make sure to mark your PR as wip or review required by making a
comment with !wip or !review required
* If you include sprites/sounds/... (assets) that you have not created
yourself specify the license and original author below.
* Ensure that you also credit them in the appropriate location /
changelog as specified in the contributor guidelines

### Asset Licenses
The following assets that **have not** been created by myself are
included in this PR:

| Path | Original Author | License |
| --- | --- | --- |
| icons/example.dmi | ExamplePerson (Example Station) | CC0 |


Fixes
[SERVER-PROD-3N](https://aurorastation.sentry.io/issues/7405041136/?seerDrawer=true)

---------

Co-authored-by: VMSolidus <evilexecutive@gmail.com>

code/modules/projectiles/ammunition/ammo_pile.dm

@@ -205,11 +205,15 @@
 	check_ammo()
 
 /obj/item/ammo_pile/proc/scatter()
+	var/turf/T = get_turf(src)
 	for(var/thing in ammo)
 		var/obj/bullet = thing
-		bullet.forceMove(get_turf(src))
+		UnregisterSignal(bullet, COMSIG_QDELETING)
+		bullet.forceMove(T)
 		bullet.throw_at_random(FALSE, 2, 7)
-		remove_ammo(bullet)
+	ammo.Cut()
+	CutOverlays()
+	qdel(src)
 
 /obj/item/ammo_pile/throw_at()
 	..()