Various fire bugfixes (#22431)

Fixes https://github.com/Aurorastation/Aurora.3/issues/22384.
Fixes https://github.com/Aurorastation/Aurora.3/issues/22389.
changes:
  - bugfix: "Fixes turf fires not spreading."
  - bugfix: "Fixes atmos fires not consistently igniting."
  - bugfix: "Fixes dead mobs burning forever."
  - bugfix: "Fixes fire_act() runtimes for multiple objects."

code/ZAS/Fire.dm

@@ -48,10 +48,12 @@ If it gains pressure too slowly, it may leak or just rupture instead of explodin
 	CHECK_COMBUSTIBLE(is_cmb, air_contents)
 	if(liquid && is_cmb)
 		IgniteTurf(liquid.amount * 10)
+		igniting = TRUE
 		QDEL_NULL(liquid)
 
 	var/obj/effect/decal/cleanable/napalm/napalm = locate() in src
 	if(napalm)
+		igniting = TRUE
 		napalm.Ignite()
 
 	if(is_cmb)