Is your feature request related to a problem? Please describe.
Currently when using items to unlock new slots, only the item stack in hand will be checked and used. This limits the number of items required for one slot unlock to the max stack size of the item, as well as being a bit more inconvenient when items are scattered across multiple stacks.

Describe the solution you'd like
When checking if the player has sufficient items, and when consuming said items, the entirety of the player inventory should be considered. With this, some limitations should also be lifted on how high the unlock cost can go.

Additional context
This was not originally implemented due to the increased complexity of checking and optionally consuming multiple stacks across the inventory rather than just a single stack, seeing as it has to be certain that it can consume the sufficient number of items before it actually does so.