Two simple changes here

• add a padding multiplier for the gas limit so that the keeper is willing to submit txs that slightly exceed the limit. I noticed a few failing txs in mainnet that are at ~510k gas, which could happen due to differences in the number of hashes. This defaults to 10% and that number should probably be fine without configuration.
• support negative target profit percentages. It turns out that for abstract-testnet, you get a gas refund at the end of the tx which is like 50% of the tx cost. However, you need to set the priority fee without counting this refund. Given that, we're systematically overestimating the needed fee.