Rough notes on the scope, subject to change:

1. add "balances cache" table which would cache the balances in order to provide quick response
2. figure out how to initialize this table after it comes to existence
   1. in one go, at startup (could lead to downtime)
   2. in the background (start the process, until it is finished respond using the "old way", once finished, switch to responding using the table)
   3. lazy? - calculate balance and store in the "balances cache" table upon request
3. the table needs to be updated on each operation that changes the balance

Other considerations:

1. state rewind
2. off-chain workerm how to sync it with background migration?