Reduce the OUSD exit fee from 0.5% to 0.25%

This proposal is to reduce the exit fee on OUSD to 0.25%. This will help keep our AMM pools balanced and ensure OUSD trades closer to its $1 peg, increasing confidence in OUSD.

Currently, a 0.5% exit fee is charged when the underlying stablecoins are redeemed from the OUSD vault. This fee is distributed as additional yield to the remaining holders of OUSD, rewarding long-term holders over short-term participants. Importantly, the exit fee serves as a security feature to prevent attackers from taking advantage of lagging oracles to siphon stablecoins from the vault in the event of mispriced underlying assets.

The 0.5% percentage was chosen to match Chainlink's deviation threshold for the USDT/USD and USDC/USD oracles. The deviation threshold represents how much the price can change before Chainlink nodes will update the price onchain. Chainlink have communicated their intent to lower their deviation thresholds to 0.25% for the USDT/USD, USDC/USD, DAI/USD oracles. Once Chainlink updates the oracles, we will be able to safely reduce our exit fee to match. We won't execute any changes until after the deviation thresholds have been updated.

You can check the status of the relevant oracles below:

https://data.chain.link/ethereum/mainnet/stablecoins/usdt-usd https://data.chain.link/ethereum/mainnet/stablecoins/usdc-usd https://data.chain.link/ethereum/mainnet/stablecoins/dai-usd

The high exit fee deters holders from redeeming with the vault even when demand falls. Currently, the price of OUSD needs to fall below $0.995 before it makes economic sense for arbitrageurs to redeem OUSD with the vault. This leads to AMM's occasionally becoming unbalanced like our Curve pool is right now. This also leads to the price of OUSD straying further from $1 than we would like. Since redemptions are a revenue generator for the protocol, we are okay with more frequent redemptions, especially if they lead to a healthier overall market.

While this proposal will likely lead to a temporary decrease in our circulating supply, I believe it will be better for OUSD long term. We want people to stay in OUSD because it's awesome, not because we're locking them in with a high exit fee.