do elo calculation on a different thread

[owobred]

Changes

Currently elo calculation is done in an async task and is massively blocking, which can upset tokio if we have a small number of cpu cores and could cause the program to lock up until elo calculation is done.

Checklist

• My code compiles
• I have committed all the files needed to build the project (check if your file is found in .gitignore)
• If I'm introducing a new step in the build process, I have documented / automated it
• I have tested my changes (minimally with one Twitch VOD)

To-do list

idk i think everything is fine, you might want to check though