Add settleAndRefund

[ChefMist]

Description

In normal cases, user would transfer the token to the vault and call vault.settle() eg.

// add liquidity 
BalanceDelta delta = poolManager.modifyLiquidity

// transfer token to vault and settle 
token0.transfer(address(vault), delta.amount0);
vault.settle(currency0);

token1.transfer(address(vault), delta.amount1);
vault.settle(currency1);

However, someone can potentially cause the txn to fail with CurrencyNotSettled() by sending 1 wei of token0 or token1 into the vault.

Fix

This PR adds settleAndRefund which handle this cases. It will be used by the v4-periphery contracts and should help to remove excess tokens in vault.

[chefburger]

rest lgtm

[ChefSnoopy]

Should we calculate the amount we need to refund in advance? then just need to execute SettlementGuard.accountDelta once if have excess token.

function settleAndRefund(Currency currency, address to)
        external
        payable
        override
        isLocked
        returns (uint256 paid, uint256 refund)
    {
        paid = currency.balanceOfSelf() - reservesOfVault[currency];
        // need to consider the case when the currencyDelta is negative ?.
        uint256 currentCurrencyDelta = (SettlementGuard.getCurrencyDelta(msg.sender, currency)).toUint256();
       
        if (paid > currentCurrencyDelta) {
            refund = paid - currentCurrencyDelta;
            paid = currentCurrencyDelta;
        }
        reservesOfVault[currency] += paid;
        SettlementGuard.accountDelta(msg.sender, currency, -(paid.toInt128()));
        if (refund > 0) {
            currency.transfer(to, refund);
        }
    }

[ChefMist]

thanks! adopted this idea since it'll save 1 sload for refund case. though did a small tweak to handle negative currency delta as settle() wont revert with SafeCastOverflow for negative balance delta

[ChefMist]

was 79085 gas previously and now dip to 56136 with Snoopy's implementation

[ChefSnoopy]

We need to think about whether there are re-entrant issues.
Let me think about this. maybe need to put this in the end after updated reservesOfVault and SettlementGuard.