Nerfs projectile piercing and makes it's chance based more on armour piercing than damage. (#22248)

- Projectiles now lose 30% of their damage for every pierce they go
through by default.

- Ship weapons only lose 5% damage on pierce. 
  
- The default chance was changed from (Pierce Chance (20%) + Damage, to
Pierce Chance (0%) + Damage / 4 + Armour Piercing.
This means the merc's STS, went from 55% chance to pierce, down to 30%,
with reduced damage when it does.

- Specialist anti-tank weapons, such as the PEAC, now have their pierce
chance multiplied by their anti-material potential.
This gives the PEAC 100% piercing chance.


<img width="327" height="261" alt="image"
src="https://github.com/user-attachments/assets/661904ec-3957-4116-a10b-e8a8fc14cd2d"
/>

code/modules/overmap/ship_weaponry/_ship_ammunition.dm

@@ -225,6 +225,7 @@
 	impact_sounds = list(BULLET_IMPACT_MEAT = SOUNDS_BULLET_MEAT, BULLET_IMPACT_METAL = SOUNDS_BULLET_METAL)
 	accuracy = 100
 	projectile_piercing = PASSMOB|PASSDOORS|PASSGLASS|PASSCLOSEDTURF|PASSWINDOW|PASSMACHINE|PASSBLOB|PASSFLAPS|PASSVEHICLE //It's a ship weapon let it try to penetrate everything.
+	pierce_decay_damage = 0.95  //Ship weapon projectiles don't lose much damage on pierce by default, but this can be set per projectile.
 	var/obj/item/ship_ammunition/ammo
 	var/primed = FALSE
 	var/hit_target = FALSE //First target we hit. Used to report if a hit was successful.