Add logic to combine references from multiple keys to a single output

[JoshuaKGoldberg]

Different keys all result in new sprites being generated, even if they're exact same. A passive routine (to be called during game pauses / etc.) combine sprites would be useful.

Options include...

• Wipe all
• Wipe directories keyed with a particular substring (e.g. "Castle")
• Wipe a particular path