Adds bullet impact particle effects! (#25177)

* Initial commit

* Cleaning up + more debris

* Adds missing trailing newline

* CI doesn't like these and starts an infinite loop it seems

* Hacky solution? I call it fixing CI

* Final fixes

code/game/objects/effects/effects.dm

@@ -148,3 +148,65 @@
 
 /obj/effect/decal/proc/on_scoop()
 	return
+
+/// These effects can be added to anything to hold particles, which is useful because Byond only allows a single particle per atom
+/obj/effect/abstract/particle_holder
+	anchored = TRUE
+	mouse_opacity = MOUSE_OPACITY_TRANSPARENT
+	layer = ABOVE_ALL_MOB_LAYER
+	vis_flags = VIS_INHERIT_PLANE
+	invisibility = FALSE
+	///typepath of the last location we're in, if it's different when moved then we need to update vis contents
+	var/last_attached_location_type
+	/// The main item we're attached to at the moment, particle holders hold particles for something
+	var/atom/parent
+	/// The mob that is holding our item
+	var/mob/holding_parent
+
+/obj/effect/abstract/particle_holder/Initialize(mapload, particle_path = null)
+	. = ..()
+	if(!loc)
+		stack_trace("particle holder was created with no loc!")
+		return INITIALIZE_HINT_QDEL
+	parent = loc
+
+	if(ismovable(parent))
+		RegisterSignal(parent, COMSIG_MOVABLE_MOVED, PROC_REF(on_move))
+	RegisterSignal(parent, COMSIG_PARENT_QDELETING, PROC_REF(on_qdel))
+
+	particles = new particle_path
+	update_visual_contents(parent)
+
+/obj/effect/abstract/particle_holder/Destroy(force)
+	if(parent)
+		UnregisterSignal(parent, list(COMSIG_MOVABLE_MOVED, COMSIG_PARENT_QDELETING))
+	QDEL_NULL(particles)
+	return ..()
+
+///signal called when parent is moved
+/obj/effect/abstract/particle_holder/proc/on_move(atom/movable/attached, atom/oldloc, direction)
+	SIGNAL_HANDLER
+	if(parent.loc.type != last_attached_location_type)
+		update_visual_contents(attached)
+
+///signal called when parent is deleted
+/obj/effect/abstract/particle_holder/proc/on_qdel(atom/movable/attached, force)
+	SIGNAL_HANDLER
+	qdel(src)//our parent is gone and we need to be as well
+
+///logic proc for particle holders, aka where they move.
+///subtypes of particle holders can override this for particles that should always be turf level or do special things when repositioning.
+///this base subtype has some logic for items, as the loc of items becomes mobs very often hiding the particles
+/obj/effect/abstract/particle_holder/proc/update_visual_contents(atom/movable/attached_to)
+	// Remove old
+	if(holding_parent && !(QDELETED(holding_parent)))
+		holding_parent.vis_contents -= src
+
+	// Add new
+	if(isitem(attached_to) && ismob(attached_to.loc)) //special case we want to also be emitting from the mob
+		var/mob/particle_mob = attached_to.loc
+		last_attached_location_type = attached_to.loc
+		particle_mob.vis_contents += src
+
+	// Readd to ourselves
+	attached_to.vis_contents |= src