Simplify storage and use of Ancient Coins

Ancient coins are often need in massive quantities for buying from NPCs and upgrading weapons. These crowd chests, and are inconvenient to carry around, as they only stack up to 9999 which is not a lot considering the costs of upgrading.

I propose that these instead be stored directly as an UI value, with no limit when they are collected. They should still be available to be "taken out" of the UI, for multiplayer purposes, by clicking a button that let's you select the amount that will be converted to item form.

Note: this proposal is different from simply storing them into the Valuables Pouch, as that space still has limitations and better used for exploration. This aims to reduce inventory management and friction when returning to base to buying from NPCs.