Overlay Caching and DMI Improvements

[Lilly-Lira]

PR Purpose and Benefit

Allows the tum overlay images to pull from multiple dmi files and makes some improvements to caching.

Development Checklist

• I have read through and accept the contributing guidelines in the Discord.
• I have submitted a project modmail or discussed my project with one of the Project Leads.
• The PR is atomic.
• I am the author of this code and I am licensing it under AGPLv3.
• All included assets are safe for work and have been documented in ATTRIBUTIONS.md.
• I am the creator of all included assets or have the permission of the creator to include them.
• I have added // RS Add/Edit or equivalent tags to my code where the changes were not already in // RS Add/Edit or equivalent tags.
• I have tested my code, both by compiling it and making sure it behaves as intended when run locally.

Development Notes

Tested and works locally and on the test server.