Implement GetBalance for extended balances which passes through to `x/bank` for non-extended denoms. This diverges from `x/evmutil` behavior which will panic on non-"akava" calls.
Add bank / account keeper mocks for testing, with mockery config for [mockery package setup](https://vektra.github.io/mockery/latest/migrating_to_packages/)
- Validate total fractional amounts in genesis type
- Validate against fractional balances such that `(sum(balances) + remainder) % conversionFactor == 0`
- Add new utility type `SplitBalance` for splitting up full balances into each
