* tried to make the balance_entry atomic, asking for feedback
* added locked select everywhere and inside the txn, it should be atomic now
* forgot about overwrite (referee vs sender entities were the same, overwriting each other), fixed it
* will now trigger refreshing cache when balance thresholds are met
* will also invalidate cache if balance gets too low (to out of funds)
* added separate balance cache with shorter TTL. need to know if i should modify it (rn its not atomic), or if low TTL is good enough, and we just fetch the value every now and then from the Database
* removed UserTier struct bcs duplicate with database
* removed subuser premium requirement (which would have lead to a merge conflict later on)
* removed user_tier artefact
* replaced cache to use AtomicF64
* a bunch of small changes
* some changes
* will merge with devel
* changed AtomicF64 to RwLock<Decimal>
* changed AtomicF64 to RwLock<Decimal>
* downgrading user when at 0.1$ or if sum_credits_used is very low
* changed caches to be more aggressive in being non-empty
* replaced Arc::clone() by reference
