Make Folia compatible and thread-safe

[Phoenix616]

With the advent of Paper's new multi-threaded fork Folia more people might try to use this utility in plugins designed for that. This ticket is for tracking that progress.

Stuff that needs to be done:

• [x] Use Folia task executor (Done with #45)
• [x] Ensure thread-safety of global maps
• [x] Ensure thread-safety of per gui instance map
• [ ] Testing!