[READY] playsound performance (#40045)

tl;dr: we have lists of playermobs on the z-level, which generally have fewer player mobs to iterate through. If we use them, we can get rid of the z-level checks too. On the off-chance that something plays a sound in nullspace, we can skip pretty much everything. The client-check can go too, there are no playermobs without a client.

code/modules/mob/dead/observer/login.dm

@@ -12,5 +12,9 @@
 		preferred_form = client.prefs.ghost_form
 		ghost_orbit = client.prefs.ghost_orbit
 
+	var/turf/T = get_turf(src)
+	if (isturf(T))
+		update_z(T.z)
+
 	update_icon(preferred_form)
 	updateghostimages()

code/modules/mob/dead/observer/logout.dm

@@ -1,4 +1,5 @@
 /mob/dead/observer/Logout()
+	update_z(null)
 	if (client)
 		client.images -= (GLOB.ghost_images_default+GLOB.ghost_images_simple)