Adds Lawyer/HoP/QM/Spy unique traitor item, the briefcase firearm mechanism (#95607)

## About The Pull Request

Lawyers, Quartermasters, and Heads of Personnels can now purchase a
`"Briefcase Embedded Firearm Trigger"` from the traitor uplink for 4 tc.

The briefcase looks like a normal, unassuming briefcase - But when any
weapon is placed inside, you gain the ability to "fire" the briefcase,
which *actually* fires the weapon.

Only the first weapon found is fired, even if it's empty.
So while you CAN put 5 pistols inside, you'd have to cycle them in and
out manually.

This works with *any* weapon that can fit inside the briefcase, which
essentially restricts it to pistols and some laser weapons.
*No*, sniper rifles won't work in the briefcase. (You can't use it to
bypass weapons that require two hands.)
*Yes*, you can also handcuff the briefcase to your wrist as normal. (Who
knows what this will allow.)

---

Also purchaseable is an 8tc `"Briefcase Embedded Firearm (Combo Deal)"`,
which comes pre-loaded with a Makarov and 0 magazines.

This variant is also available to all Spies as a medium difficulty
reward.

--- 

Additionally I changed the boot-dagger's examine tell to only show to
people holding the item.
When I was implementing the briefcase gun I made the examine tell only
show while held and I thought "well, the boot-dagger should follow the
same logic". They're meant to be stealth objects so being able to figure
it out from across the room feels weird.

## Why It's Good For The Game

This was a random idea someone threw out that I thought fit the vibe and
gameplay of traitors and spies really well.
It's a very espionage-y idea, very James Bond. 

It will definitely catch a lot of people off guard. It basically allows
the Lawyer to walk around with a pistol or revolver drawn at all times.
I'm a bit worried it'll be too potent combined with handcuffs (nodrop
revolver?), but the Lawyer doesn't get many Ws so maybe it's fine.

## Changelog

🆑 Melbert
add: Traitor Lawyers, Quartermasters, and Heads of Personnels can now
purchase a "Briefcase Embedded Firearm Trigger" from the uplink for 4tc
- a briefcase that allows any weapon stored within to be fired by
"firing" the briefcase itself. Weapon sizes are restricted to whatever
fits in a briefcase, meaning it practically only works with pistols and
some laser weapons. It has a subtle examine tell that only appears while
being held.
add: Also available for 8tc is a combo deal that comes pre-loaded with a
Makarov. This can also appear as a medium Spy reward.
balance: The Spy item "boot dagger"'s examine tell now only appears if
you're examining them WHILE holding them.
/🆑

code/game/objects/items/storage/briefcase.dm

@@ -179,3 +179,22 @@
 	remote.pad = WEAKREF(src.pad)
 	to_chat(user, span_notice("You link [pad] to [remote]."))
 	return ITEM_INTERACT_BLOCKING
+
+/obj/item/storage/briefcase/gun
+	storage_type = /datum/storage/briefcase/gun
+
+/obj/item/storage/briefcase/gun/ranged_interact_with_atom(atom/interacting_with, mob/living/user, list/modifiers)
+	for(var/obj/item/gun/weapon in src)
+		return weapon.try_fire_gun(interacting_with, user, list2params(modifiers))
+	return NONE
+
+/obj/item/storage/briefcase/gun/examine_more(mob/user)
+	. = ..()
+	if(user.is_holding(src))
+		. += span_notice("Upon closer inspection, you notice a hole in the side of the briefcase.")
+
+/obj/item/storage/briefcase/gun/preloaded
+
+/obj/item/storage/briefcase/gun/preloaded/PopulateContents()
+	new /obj/item/gun/ballistic/automatic/pistol(src)
+	return ..()