Dynamic Exit Fee

Our current exit fee (set to 0.5%) is kind of a catch-all to prevent abuse of our vault contract, deter users from redeeming, and provide a potential revenue source that could increase the APY and/or accrue to governance token holders. In our recent discussion about removing oracles from the rebase calculation, @tomlinton proposed making the exit fee variable based on asset prices in a way that "makes it net-zero to exploit in case of peg loss".

Based on the currencies you are receiving for your OUSD, we use the oracles to calculate the exit fee and make the whole thing viewable so we can display the exit fee in real time without gas... We don't care about stablecoins deviating from their peg unless someone is redeeming, we can just assume they'll always return to 1.

Start with linked issue #92 and the vault contract's current 0.5% exit-fee implementation, then trace the oracle inputs used for redemption and rebase calculations. Confirm the desired pricing, peg-loss, gas-free view, and governance or APY behavior with maintainers; no implementation files or tests are named, so completion criteria remain to be specified.