World files only in tmpfs/shared memory

### Enhancement Type

A completely new feature

### Describe the enhancement

It would be spectacularly nice if i could store the world folder in RAM so that worldgen doesn't cause as much lag. This feature would obviously require the end user to use backups AND would require that the server restore from backup as a part of startup. Not sure how simple this would be to implement using what you've got, but it would be really nice, as the custom container i build now does this and I'd love to switch to your FAR FAR more mature and organized image here, but don't particularly want to go back to world on disk. :D

The issue names no files, tests, or entry points. Start by mapping the image's startup, backup, restore, and world-directory handling, then verify how a tmpfs/shared-memory world would be configured and recovered on startup. Done means documented, tested behavior that preserves the stated backup requirement.

Written by the indexing model from the issue text.