Fixes speed potions behaving super inconsistently on magboots, duffelbags and laptops (#91415)

## About The Pull Request

The issue was threefold, first speed potions sent the comsig before
actually applying which could be abused to make items not have a
slowdown without spending it or coloring them by using it on them in a
state when they don't have a slowdown (i.e. disabled magboots). Magboots
``initial()``'d their slowdown which could break them if they somehow
got it negative, but I believe that didn't happen in actual gameplay.
And I've made duffelbags and laptops have their open slowdown set to 0
similarly to magboots when a speed potion is applied to them. Last one
may be a balance change, depending on the original intent, but I'm going
off their pre-rework behavior here (and it generally feels weird to be
the case when they get unslowdowned and then it gets reapplied when you
close and open them)

- Closes #91381

## Changelog
🆑
fix: Fixed speed potions behaving super inconsistently on magboots,
duffelbags and laptops
/🆑

code/modules/modular_computers/computers/item/laptop.dm

@@ -24,6 +24,12 @@
 	var/w_class_open = WEIGHT_CLASS_BULKY
 	var/slowdown_open = 1
 
+/obj/item/modular_computer/laptop/Initialize(mapload)
+	. = ..()
+	if(start_open && !screen_on)
+		toggle_open()
+	RegisterSignal(src, COMSIG_SPEED_POTION_APPLIED, PROC_REF(on_speed_potioned))
+
 /obj/item/modular_computer/laptop/examine(mob/user)
 	. = ..()
 	if(screen_on)
@@ -39,11 +45,11 @@
 
 	return CONTEXTUAL_SCREENTIP_SET
 
-/obj/item/modular_computer/laptop/Initialize(mapload)
-	. = ..()
-
-	if(start_open && !screen_on)
-		toggle_open()
+/// Signal handler for [COMSIG_SPEED_POTION_APPLIED]. Speed potion removes the open slowdown
+/obj/item/modular_computer/laptop/proc/on_speed_potioned(datum/source)
+	SIGNAL_HANDLER
+	// Don't need to touch the actual slowdown here, since the speed potion does it for us
+	slowdown_open = 0
 
 /obj/item/modular_computer/laptop/update_icon_state()
 	if(!screen_on)
@@ -108,14 +114,15 @@
 /obj/item/modular_computer/laptop/proc/toggle_open(mob/living/user=null)
 	if(screen_on)
 		to_chat(user, span_notice("You close \the [src]."))
-		slowdown = initial(slowdown)
+		slowdown -= slowdown_open
 		update_weight_class(initial(w_class))
 		drag_slowdown = initial(drag_slowdown)
 	else
 		to_chat(user, span_notice("You open \the [src]."))
-		slowdown = slowdown_open
+		slowdown += slowdown_open
 		update_weight_class(w_class_open)
 		drag_slowdown = slowdown_open
+
 	if(isliving(loc))
 		var/mob/living/localmob = loc
 		localmob.update_equipment_speed_mods()