fixes a big harddel source (#83987)

## About The Pull Request
this hard delete would happen everytime a player joins/observers the
round. upon using the ref tracker i discovered this problem was caused
by movable/screens not cleaning up after their owning huds if it gets
deleted. i didnt weakref it was cause it meant id have to resolve it in
so many places, but if weakrefing is preferable i will do it

![image](https://github.com/tgstation/tgstation/assets/138636438/d4b5465e-85b6-4e79-80a7-551684bdd831)


## Why It's Good For The Game
fixes a hard delete

code/_onclick/hud/new_player.dm

@@ -63,8 +63,7 @@
 
 ///Set the HUD in New, as lobby screens are made before Atoms are Initialized.
 /atom/movable/screen/lobby/New(loc, datum/hud/our_hud, ...)
-	if(our_hud)
-		hud = our_hud
+	set_new_hud(our_hud)
 	return ..()
 
 ///Run sleeping actions after initialize

code/_onclick/hud/parallax/parallax.dm

@@ -275,7 +275,7 @@ INITIALIZE_IMMEDIATE(/atom/movable/screen/parallax_layer)
 	. = ..()
 	// Parallax layers are independant of hud, they care about client
 	// Not doing this will just create a bunch of hard deletes
-	hud = null
+	set_new_hud(hud_owner = null)
 
 	if(template)
 		return

code/_onclick/hud/screen_objects.dm

@@ -45,8 +45,9 @@
 
 /atom/movable/screen/Initialize(mapload, datum/hud/hud_owner)
 	. = ..()
-	if(hud_owner && istype(hud_owner))
-		hud = hud_owner
+	if(isnull(hud_owner)) //some screens set their hud owners on /new, this prevents overriding them with null post atoms init
+		return
+	set_new_hud(hud_owner)
 
 /atom/movable/screen/Destroy()
 	master_ref = null
@@ -72,10 +73,25 @@
 /atom/movable/screen/proc/component_click(atom/movable/screen/component_button/component, params)
 	return
 
+///setter used to set our new hud
+/atom/movable/screen/proc/set_new_hud(datum/hud/hud_owner)
+	if(hud)
+		UnregisterSignal(hud, COMSIG_QDELETING)
+	if(isnull(hud_owner))
+		hud = null
+		return
+	hud = hud_owner
+	RegisterSignal(hud, COMSIG_QDELETING, PROC_REF(on_hud_delete))
+
 /// Returns the mob this is being displayed to, if any
 /atom/movable/screen/proc/get_mob()
 	return hud?.mymob
 
+/atom/movable/screen/proc/on_hud_delete(datum/source)
+	SIGNAL_HANDLER
+
+	set_new_hud(hud_owner = null)
+
 /atom/movable/screen/text
 	icon = null
 	icon_state = null