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/modules/research/stock_parts.dm

@@ -6,13 +6,13 @@ If you create T5+ please take a pass at mech_fabricator.dm. The parts being good
 	name = "stock part"
 	desc = "What?"
 	icon = 'icons/obj/devices/stock_parts.dmi'
+	///The generic category type that the stock part belongs to.  Generic objects that should not be instantiated should have the same type and abstract_type
+	abstract_type = /obj/item/stock_parts
 	w_class = WEIGHT_CLASS_SMALL
 	var/rating = 1
 	///Used when a base part has a different name to higher tiers of part. For example, machine frames want any servo and not just a micro-servo.
 	var/base_name
 	var/energy_rating = 1
-	///The generic category type that the stock part belongs to.  Generic objects that should not be instantiated should have the same type and abstract_type
-	var/abstract_type = /obj/item/stock_parts
 
 /obj/item/stock_parts/Initialize(mapload)
 	. = ..()