use async*/await*

[letmejustputthishere]

use new language feature to extract async methods without issuing self messages https://forum.dfinity.org/t/generational-gc-on-playground-and-new-async-await-weekly-motoko-updates/17270?u=cryptoschindler

[letmejustputthishere]

this is helpful for all the canister internal methods that we await, e.g. in our main.mo when we await calls to the class methods. everytime we do this we issue a self call, which fills up the queue