PriceImpact - prevent bad results

[brunoguerios]

PriceImpact uses an approximation method (ABA) to estimate the price impact of an action (add/remove liquidity unbalanced/single token)

We currently only throw errors for actions where internal queries indeed fail (e.g. add liquidity unbalanced with amountsIn higher than pool balance)

The problem is that there are scenarios that internal queries won't fail, but results are far off the "correct" price impact (e.g. add liquidity unbalanced with amountsIn slightly below pool balance)

With the premise that it's better to show no result rather than a bad result, it would be nice to evaluate which scenarios could potentially return bad results and prevent them to be returned.