feat(Party): add gas refunds for voting

[0xble]

Motivation

Needing to pay gas to vote on a proposal punishes active governance. It is especially insidious since voting against a proposal (i.e. not voting at all) does not cost gas while voting for a proposal does, which skews incentives toward inaction.

And just very simply, paying gas sucks.

Solution

If enabled by a host, voters will be refunded the cost of gas from the Party's balance of ETH for voting on proposals.

Here is the core logic for calculating refund amounts:

uint256 startGas = gasleft();

// ... Rest of logic for accepting proposals

// Only refund if the party has ETH.
uint256 balance = address(this).balance;
if (balance == 0) return;

// Calculate the refund amount.
uint256 baseFee = _min(block.basefee, maxBaseFee);
uint256 gasPrice = _min(tx.gasprice, baseFee + maxPriorityFee);
uint256 gasUsed = _min(startGas - gasleft() + baseGasUsed, maxGasUsed);
uint256 refund = _min(gasPrice * gasUsed, balance);

// Transfer the refund. Do not revert if it fails.
(bool wasRefundSent, ) = tx.origin.call{ value: refund }("");

emit GasRefunded(tx.origin, refund, wasRefundSent);

[height]

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