Adding unchecked directive can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

For example:

https://github.com/pooltogether/v4-periphery/blob/0e94c54774a6fce29daf9cb23353208f80de63eb/contracts/TwabRewards.sol#L153-L153

uint256 _amount = _numberOfEpochs * _promotion.tokensPerEpoch;

_numberOfEpochs is uint8
_promotion.tokensPerEpoch is uint216

_numberOfEpochs * _promotion.tokensPerEpoch will never overflow.