New powernet light flicker (#92567)

## About The Pull Request

Changes light flicker to be an overlay instead of a rapid turning on/off
of the light itself. It acts similar to a brownout and delayed restart
of the light.

The introduction of lights flickering when the powernet is hit by a bomb
is a cool effect, but makes it very apparent the current flicker
method's limitations. Rapid cycling of machinery on/off as fast as 0.5
seconds, spanning over dozens of lights at a time leads to the subsystem
not being able to keep up with the lighting changes. It ultimately
results in just a single broken looking change of lighting

<details>
<summary>Screenshots/Videos</summary>
Before:


https://github.com/user-attachments/assets/8237e72e-1edc-4423-b48b-8dd403ee3111


https://github.com/user-attachments/assets/f3a3d481-61fa-4fd9-b51c-3c1e080e129c

After:


https://github.com/user-attachments/assets/0fa2bbfd-4ca7-422a-8cd1-b6b738addb0f


https://github.com/user-attachments/assets/8b8b10b9-912a-4476-9a11-985f79228500

</details>

## Why It's Good For The Game

The powernet flicker effect looks better (and also now has an electrical
sizzle sound)

## Changelog

🆑 LT3
code: Improved powernet light flickering
/🆑

code/modules/mob/living/basic/space_fauna/revenant/revenant_abilities.dm

@@ -192,7 +192,7 @@
 		if(window.fulltile)
 			new /obj/effect/temp_visual/revenant/cracks(window.loc)
 	for(var/obj/machinery/light/light in victim)
-		light.flicker(20) //spooky
+		light.flicker(rand(3, 5)) //spooky
 
 //Malfunction: Makes bad stuff happen to robots and machines.
 /datum/action/cooldown/spell/aoe/revenant/malfunction

code/modules/power/lighting/light.dm

@@ -180,6 +180,9 @@
 
 	var/area/local_area = get_room_area()
 
+	if(flickering)
+		. += mutable_appearance(overlay_icon, "[base_state]_flickering")
+		return
 	if(low_power_mode || major_emergency || (local_area?.fire))
 		. += mutable_appearance(overlay_icon, "[base_state]_emergency")
 		return
@@ -225,7 +228,11 @@
 		if(reagents)
 			START_PROCESSING(SSmachines, src)
 		var/area/local_area = get_room_area()
-		if (local_area?.fire)
+		if (flickering)
+			brightness_set = brightness * bulb_low_power_brightness_mul
+			power_set = bulb_low_power_pow_mul
+			color_set = nightshift_light_color
+		else if (local_area?.fire)
 			color_set = fire_colour
 			power_set = fire_power
 			brightness_set = fire_brightness
@@ -500,27 +507,36 @@
 		)
 	return TRUE
 
-/obj/machinery/light/proc/flicker(amount = rand(10, 20))
+/obj/machinery/light/proc/flicker(amount = 1)
 	set waitfor = FALSE
 	if(flickering || !on || status != LIGHT_OK)
 		return
 
 	. = TRUE // did we actually flicker? Send this now because we expect immediate response, before sleeping.
-	flickering = TRUE
+	set_light(
+		l_range = brightness * bulb_low_power_brightness_mul,
+		l_power = bulb_low_power_pow_mul,
+		l_color = nightshift_light_color,
+	)
+	cut_overlays(src)
+	stoplag(0.7 SECONDS)
+	if(prob(30))
+		do_sparks(number = 2, cardinal_only = TRUE, source = src)
+
 	for(var/i in 1 to amount)
 		if(status != LIGHT_OK || !has_power())
 			break
-		on = !on
+		flickering = !flickering
 		update(FALSE)
-		stoplag(rand(0.5 SECONDS, 1.5 SECONDS))
+		stoplag(pick(list(2 SECONDS, 4 SECONDS, 6 SECONDS)))
 
 	if(has_power())
 		on = (status == LIGHT_OK)
 	else
 		on = FALSE
 
-	update(FALSE)
 	flickering = FALSE
+	update(FALSE)
 
 // ai attack - make lights flicker, because why not
 

code/modules/power/powernet.dm

@@ -111,7 +111,6 @@
 		return
 
 	flickering = TRUE
-	var/most_flickers = 1
 	for(var/obj/machinery/power/terminal/terminal in nodes)
 		if(!istype(terminal.master, /obj/machinery/power/apc))
 			continue
@@ -123,12 +122,10 @@
 		if(!prob(flicker_prob))
 			continue
 
-		var/flicker_count = rand(1, 3)
-		most_flickers = max(most_flickers, flicker_count)
 		var/obj/machinery/power/apc/apc = terminal.master
 		for(var/obj/machinery/light/light as anything in apc.get_lights())
-			light.flicker(flicker_count)
+			light.flicker(amount = 1)
 			CHECK_TICK
 
 	// don't let another flicker propagation until our slowest area is done (with some added leeway)
-	addtimer(VARSET_CALLBACK(src, flickering, FALSE), most_flickers * 2 SECONDS)
+	addtimer(VARSET_CALLBACK(src, flickering, FALSE), 9 SECONDS)