Fixes Permanent Fire Visual Bug (#79326)

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## About The Pull Request

There was a bug where the fire visual effect would remain even after the
fire status effect was removed. It happened most often with lava, but
apparently happened in some other circumstances too. I believe I have
tracked down and fixed all sources of the bug. The culprit was
`/mob/living/proc/update_fire`. It was searching for a base
`/datum/status_effect/fire_handler` status effect, when it should have
been looking for `/datum/status_effect/fire_handler/fire_stacks`. I
tested it with lava, and it fixed the bug. If anyone knows of a reliable
way to cause the bug without lava, I would be happy to test it there as
well. Closes #73283.

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:cl:
fix: The fire visual on mobs should no longer persist after the fire has
been extinguished.
/:cl:

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code/modules/mob/living/living.dm

@@ -1564,9 +1564,9 @@ GLOBAL_LIST_EMPTY(fire_appearances)
 	return fire_status.ignite(silent)
 
 /mob/living/proc/update_fire()
-	var/datum/status_effect/fire_handler/fire_handler = has_status_effect(/datum/status_effect/fire_handler)
-	if(fire_handler)
-		fire_handler.update_overlay()
+	var/datum/status_effect/fire_handler/fire_stacks/fire_stacks = has_status_effect(/datum/status_effect/fire_handler/fire_stacks)
+	if(fire_stacks)
+		fire_stacks.update_overlay()
 
 /**
  * Extinguish all fire on the mob