Implements shared particle holders, re-adds slimed status particles using the new system (#87892)

## About The Pull Request

Partial revert of #86701
Implements a shared holder particle system, somewhat inspired by
https://github.com/Baystation12/Baystation12/pull/34014 (thanks Kapu).
Atoms can be assigned "shared" particles via add_shared_particles, with
an optional "alternate" key passed as a second arg if you're planning to
edit the returned particle holder (for example, color it like slimed
status does). Removing is done via remove_shared_particles with an
option to delete the shared holder if nothing is using it anymore (on by
default). This system should be prioritized over normal particle holders
when a lot of entities would be using a certain particle effect (like
fires) as it conserves a lot of clientside performance.

Burning, acid, decaying, firestacks and slimed status now use this
system which should help with clientside performance and amount of atoms
created/destroyed.

## Why It's Good For The Game

Less clientside lag.

## Changelog
🆑
refactor: Firestacks, burning/acid/decaying effects and (brought back
after being temporarily removed) slimed status effects now use a new
"shared" particles system, which should considerably improve client
performance when encountering a lot of burning/slimed entities.
/🆑

---------

Co-authored-by: Ghom <42542238+Ghommie@users.noreply.github.com>

code/datums/components/acid.dm

@@ -25,8 +25,10 @@ GLOBAL_DATUM_INIT(acid_overlay, /mutable_appearance, mutable_appearance('icons/e
 	var/turf_acid_ignores_mobs = FALSE
 	/// The ambient sound of acid eating away at the parent [/atom].
 	var/datum/looping_sound/acid/sizzle
-	/// Particle holder for acid particles (sick)
+	/// Particle holder for acid particles (sick). Still utilized over shared holders because they're movable-only
 	var/obj/effect/abstract/particle_holder/particle_effect
+	/// Particle type we're using for cleaning up our shared holder
+	var/particle_type
 	/// The proc used to handle the parent [/atom] when processing. TODO: Unify damage and resistance flags so that this doesn't need to exist!
 	var/datum/callback/process_effect
 
@@ -68,8 +70,13 @@ GLOBAL_DATUM_INIT(acid_overlay, /mutable_appearance, mutable_appearance('icons/e
 
 	sizzle = new(atom_parent, TRUE)
 	if(acid_particles)
-		// acid particles look pretty bad when they stack on mobs, so that behavior is not wanted for items
-		particle_effect = new(atom_parent, acid_particles, isitem(atom_parent) ? NONE : PARTICLE_ATTACH_MOB)
+		if (ismovable(parent))
+			var/atom/movable/movable_parent = parent
+			movable_parent.add_shared_particles(acid_particles, "[acid_particles]_[isitem(parent)]", isitem(parent) ? NONE : PARTICLE_ATTACH_MOB)
+			particle_type = acid_particles
+		else
+			// acid particles look pretty bad when they stack on mobs, so that behavior is not wanted for items
+			particle_effect = new(atom_parent, acid_particles, isitem(atom_parent) ? NONE : PARTICLE_ATTACH_MOB)
 	START_PROCESSING(SSacid, src)
 
 /datum/component/acid/Destroy(force)
@@ -78,6 +85,9 @@ GLOBAL_DATUM_INIT(acid_overlay, /mutable_appearance, mutable_appearance('icons/e
 		QDEL_NULL(sizzle)
 	if(particle_effect)
 		QDEL_NULL(particle_effect)
+	if (ismovable(parent) && particle_type)
+		var/atom/movable/movable_parent = parent
+		movable_parent.remove_shared_particles("[particle_type]_[isitem(parent)]")
 	process_effect = null
 	return ..()
 

code/datums/components/burning.dm

@@ -8,8 +8,10 @@ GLOBAL_DATUM_INIT(fire_overlay, /mutable_appearance, mutable_appearance('icons/e
 /datum/component/burning
 	/// Fire overlay appearance we apply
 	var/fire_overlay
-	/// Particle holder for fire particles, if any
+	/// Particle holder for fire particles, if any. Still utilized over shared holders because they're movable-only
 	var/obj/effect/abstract/particle_holder/particle_effect
+	/// Particle type we're using for cleaning up our shared holder
+	var/particle_type
 
 /datum/component/burning/Initialize(fire_overlay = GLOB.fire_overlay, fire_particles = /particles/smoke/burning)
 	if(!isatom(parent))
@@ -25,9 +27,14 @@ GLOBAL_DATUM_INIT(fire_overlay, /mutable_appearance, mutable_appearance('icons/e
 		return
 
 	src.fire_overlay = fire_overlay
-	if(fire_particles)
-		// burning particles look pretty bad when they stack on mobs, so that behavior is not wanted for items
-		particle_effect = new(atom_parent, fire_particles, isitem(atom_parent) ? NONE : PARTICLE_ATTACH_MOB)
+	if (fire_particles)
+		if(ismovable(parent))
+			var/atom/movable/movable_parent = parent
+			// burning particles look pretty bad when they stack on mobs, so that behavior is not wanted for items
+			movable_parent.add_shared_particles(fire_particles, "[fire_particles]_[isitem(parent)]", isitem(parent) ? NONE : PARTICLE_ATTACH_MOB)
+			particle_type = fire_particles
+		else
+			particle_effect = new(atom_parent, fire_particles)
 	START_PROCESSING(SSburning, src)
 
 /datum/component/burning/Destroy(force)
@@ -35,6 +42,9 @@ GLOBAL_DATUM_INIT(fire_overlay, /mutable_appearance, mutable_appearance('icons/e
 	fire_overlay = null
 	if(particle_effect)
 		QDEL_NULL(particle_effect)
+	if (ismovable(parent) && particle_type)
+		var/atom/movable/movable_parent = parent
+		movable_parent.remove_shared_particles("[particle_type]_[isitem(parent)]")
 	return ..()
 
 /datum/component/burning/RegisterWithParent()

code/datums/components/food/decomposition.dm

@@ -27,8 +27,6 @@
 	var/produce_ants = FALSE
 	/// Stink particle type, if we are supposed to create stink particles
 	var/stink_particles
-	/// Stink particle holder
-	var/obj/effect/abstract/particle_holder/particle_effect
 
 /datum/component/decomposition/Initialize(mapload, decomp_req_handle, decomp_flags = NONE, decomp_result, ant_attracting = FALSE, custom_time = 0, stink_particles = /particles/stink)
 	if(!ismovable(parent) || !HAS_TRAIT(parent, TRAIT_GERM_SENSITIVE))
@@ -52,9 +50,11 @@
 	src.stink_particles = stink_particles
 
 /datum/component/decomposition/Destroy()
-	. = ..()
-	if(particle_effect)
-		QDEL_NULL(particle_effect)
+	remove_timer()
+	if (stink_particles)
+		var/atom/movable/movable_parent = parent
+		movable_parent.remove_shared_particles("[stink_particles]_[isitem(parent)]")
+	return ..()
 
 /datum/component/decomposition/RegisterWithParent()
 	RegisterSignal(parent, COMSIG_ATOM_GERM_EXPOSED, PROC_REF(start_timer))
@@ -78,17 +78,13 @@
 	// If all other checks fail, then begin decomposition.
 	decomp_timerid = addtimer(CALLBACK(src, PROC_REF(decompose)), time_remaining, TIMER_STOPPABLE | TIMER_UNIQUE)
 
-	// Also start the stinking timer, if have stink particles and aren't stinking yet
-	if(!stink_particles || particle_effect)
+	// Also start the stinking timer, if have stink particles
+	if(!stink_particles)
 		return
 
 	var/stink_time = max(0, time_remaining - (original_time * 0.5))
 	stink_timerid = addtimer(CALLBACK(src, PROC_REF(stink_up)), stink_time, TIMER_STOPPABLE | TIMER_UNIQUE)
 
-/datum/component/decomposition/Destroy()
-	remove_timer()
-	return ..()
-
 /// Returns the time remaining in decomp, either from our potential timer or our own value, whichever is more useful
 /datum/component/decomposition/proc/get_time()
 	if(!decomp_timerid)
@@ -108,11 +104,12 @@
 
 /datum/component/decomposition/proc/stink_up()
 	stink_timerid = null
-	// Neither should happen, but to be sure
-	if(particle_effect || !stink_particles)
+	// Shouldn't happen, but to be sure
+	if(!stink_particles)
 		return
 	// we don't want stink lines on mobs (even though it'd be quite funny)
-	particle_effect = new(parent, stink_particles, isitem(parent) ? NONE : PARTICLE_ATTACH_MOB)
+	var/atom/movable/movable_parent = parent
+	movable_parent.add_shared_particles(stink_particles, "[stink_particles]_[isitem(parent)]", isitem(parent) ? NONE : PARTICLE_ATTACH_MOB)
 
 /datum/component/decomposition/proc/decompose()
 	decomp_timerid = null