Medical stacks (#20824)

* Fixes gauze upgrading

* Fixes accidental line removal

* Unessassary boolean

* shortens code, adds flag to /stack/medical

* Clarity and proper inhertance

code/game/objects/items/stacks/stack.dm

@@ -31,6 +31,8 @@
 	var/table_type
 	/// If this stack has a dynamic icon_state based on amount / max_amount
 	var/dynamic_icon_state = FALSE
+	/// if true, then this item can't stack with subtypes
+	var/parent_stack = FALSE
 
 /obj/item/stack/Initialize(mapload, new_amount, merge = TRUE)
 	. = ..()
@@ -360,7 +362,7 @@
 	use(amount)
 
 /obj/item/stack/attackby(obj/item/W, mob/user, params)
-	if(istype(W, merge_type))
+	if((!parent_stack && istype(W, merge_type)) || (parent_stack && W.type == type))
 		var/obj/item/stack/S = W
 		merge(S)
 		to_chat(user, "<span class='notice'>Your [S.name] stack now contains [S.get_amount()] [S.singular_name]\s.</span>")