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/datums/brain_damage/brain_trauma.dm

@@ -4,6 +4,8 @@
 // of the trauma.
 
 /datum/brain_trauma
+	/// Tracks abstract types of brain traumas, useful for determining traumas that should not exist
+	abstract_type = /datum/brain_trauma
 	var/name = "Brain Trauma"
 	var/desc = "A trauma caused by brain damage, which causes issues to the patient."
 	var/scan_desc = "generic brain trauma" //description when detected by a health scanner
@@ -15,9 +17,6 @@
 	var/random_gain = TRUE //can this be gained through random traumas?
 	var/resilience = TRAUMA_RESILIENCE_BASIC //how hard is this to cure?
 
-	/// Tracks abstract types of brain traumas, useful for determining traumas that should not exist
-	var/abstract_type = /datum/brain_trauma
-
 /datum/brain_trauma/Destroy()
 	// Handles our references with our brain
 	brain?.remove_trauma_from_traumas(src)