moves abstract_type up to datum, spawners wont spawn them (#92909)

## About The Pull Request
moves all implementations (im aware of) for "Im a parent type dont spawn
me please" to the datum layer to standardized behavior
adds a standerized proc for filtering out "bad" items that we dont want
spawning. applies to it the subtype vendor, gifts, and a new spawner and
mystery box for a random gun (neither playerfacing)
"port" of https://github.com/shiptest-ss13/Shiptest/pull/4621



https://github.com/user-attachments/assets/22f6f0b2-b44e-411a-b3dc-6b97dc0287aa

small warning: I dont have EVERY abstract type defined right now but,
ive done a good enough job for now. Im tired of data entry rn
## Why It's Good For The Game
standardizing behavior. Might be a micro hit to performance however

having this lets us not rely on icon state to determine whether
something is a parent type and makes it much easier to tell something is
a parent type (could be applied further to things like admin spawning
menus and things like that).

need feedback on if this is actually good for the game.
## Changelog
🆑
add: Soda cans show up in the silver slime drink table.
add: Examine tag for items that are not mean to show up ingame.
refactor: Standardizes how gifts rule out abstract types.
fix: gifts no longer check if something has an inhand, massively
expanding the list of potential items.
/🆑

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

@@ -19,6 +19,7 @@
 
 //  Generic non-item
 /obj/item/storage/bag
+	abstract_type = /obj/item/storage/bag
 	slot_flags = ITEM_SLOT_BELT
 	w_class = WEIGHT_CLASS_BULKY
 	storage_type = /datum/storage/bag

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

@@ -7,6 +7,7 @@
 	worn_icon_state = "utility"
 	lefthand_file = 'icons/mob/inhands/equipment/belt_lefthand.dmi'
 	righthand_file = 'icons/mob/inhands/equipment/belt_righthand.dmi'
+	abstract_type = /obj/item/storage/belt
 	slot_flags = ITEM_SLOT_BELT
 	attack_verb_continuous = list("whips", "lashes", "disciplines")
 	attack_verb_simple = list("whip", "lash", "discipline")

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

@@ -15,6 +15,7 @@
 
 /obj/item/storage/fancy
 	icon = 'icons/obj/food/containers.dmi'
+	abstract_type = /obj/item/storage/fancy
 	resistance_flags = FLAMMABLE
 	custom_materials = list(/datum/material/cardboard = SHEET_MATERIAL_AMOUNT)
 	/// Used by examine to report what this thing is holding.

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

@@ -1,6 +1,7 @@
 /obj/item/storage
 	name = "storage"
 	icon = 'icons/obj/storage/storage.dmi'
+	abstract_type = /obj/item/storage
 	w_class = WEIGHT_CLASS_NORMAL
 	interaction_flags_click = ALLOW_RESTING | FORBID_TELEKINESIS_REACH
 	action_slots = ALL