[ad-hoc] [2] only reset cached balances and liabilities if pruneOps > 0, reducing unnecessary network calls

[nikhilsaraf]

• speeds up update loop cycle by ~10% (~3.4s to ~3.0s) for the mirror strategy in the case where there's no pruneOps such as the mirror strategy
• buysell when there's no prune ops reduced to ~2.8s (not sure what it was before)