Ensure that casings are stackable

[Aivean]

Summary

SUMMARY: Bugfixes "Ensure that casings are stackable (fixes pickup performance issues)"

Purpose of change

Fix #44469.

The problem is two-fold:

1. Some casings are not stackable. When large stacks ammo are deconstructed into non-stackable components, it creates huge amounts of individual items (4000+ casings in the Trying to pick .22 casings lags the whole game to a halt #44469)
2. Inventory management is slow and generally is not able to handle 4000+ individual items. Specifically, such items are added one by one, and each addition invalidates inventory cache, leading to the full recalculation of Character::drop_invalid_inventory()

Describe the solution

This PR addresses only the first issue. I made all currently existing casings stackable and added a unit test to (hopefully) ensure that all casings added in the future are also stackable.

The downside of this fix is that already disassembled ammo is still saved as individual items and will be slow to pick up. However, I think the issue is uncommon enough to bother with adding any kind of migration.

Describe alternatives you've considered

Alternative would be to address second part of the problem: inventory speed. Unfortunately, fixing that is by no means trivial. There is an ongoing discussion regarding some of the ways such improvements could be done.

Testing

Added unit test, verified that it was failing before the change and succeeds after.
Loaded the save file from #44469, disassembled .22 ammo into the stack of 4000+, picked it up instantaneously.

Additional context

After:

[paulenka-aleh]

Awesome! Any chance for rags and glass shards?