Refactor sync/caching #1251
Description
This was one of the main reasons for porting the source code to TypeScript. So now it's time to actually refactor and clean up the code that is virtually impossible to quickly debug due to extended Promise chains, some of which span 20+ functions. (Just FYI, for new contributors: when that code was written, Promise wasn't even part of JavaScript itself, but only a half-standardized spec which we used via a utility library).
My proposal would be to use async/await as much as possible instead.
Edit: I have added sub issues for everything I could find that is related and would be good to close on the way.