lazily initialize /datum/element/weapon_description on examine (#92489)

## About The Pull Request

currently, `/datum/element/weapon_description` is added during every
single item init, even tho it only ever affects examines. i noticed
while looking at tracy traces downstream that it spent a bit much time
adding the weapon description, so why not just lazily initialize it
during examine instead?

direct port of the same thing from
https://github.com/Monkestation/Monkestation2.0/pull/7502

## Why It's Good For The Game

less wasted time during item init

## Changelog
🆑
code: Item weapon description elements are now initialized when first
examined, instead of immediately upon initialization.
/🆑

code/__DEFINES/obj_flags.dm

@@ -51,6 +51,8 @@
 #define NO_BLOOD_ON_ITEM (1 << 19)
 /// Whether this item should skip the /datum/component/fantasy applied on spawn on the RPG event. Used on things like stacks
 #define SKIP_FANTASY_ON_SPAWN (1<<20)
+/// If an item has had its /datum/element/weapon_description initialized or not.
+#define WEAPON_DESCRIPTION_INITIALIZED (1<<21)
 
 // Flags for the clothing_flags var on /obj/item/clothing
 

code/game/objects/items.dm

@@ -284,8 +284,6 @@
 		if(damtype == BRUTE)
 			hitsound = SFX_SWING_HIT
 
-	add_weapon_description()
-
 	SEND_GLOBAL_SIGNAL(COMSIG_GLOB_NEW_ITEM, src)
 
 	setup_reskinning()
@@ -499,6 +497,13 @@
 /obj/item/examine_descriptor(mob/user)
 	return "item"
 
+/obj/item/examine(mob/user)
+	// lazily initialize the weapon description element if it hasn't been already
+	if(!(item_flags & WEAPON_DESCRIPTION_INITIALIZED))
+		add_weapon_description()
+		item_flags |= WEAPON_DESCRIPTION_INITIALIZED
+	return ..()
+
 /obj/item/examine_more(mob/user)
 	. = ..()
 	if(HAS_TRAIT(user, TRAIT_RESEARCH_SCANNER))