`_nextPromotionId/_latestPromotionId` calculation can be done more efficiently

[code423n4]

Handle

0x0x0x

Vulnerability details

https://github.com/pooltogether/v4-periphery/blob/b520faea26bcf60371012f6cb246aa149abd3c7d/contracts/TwabRewards.sol#L98-L99

Here promotion id calculations are done as follows:

uint256 _nextPromotionId = _latestPromotionId + 1;
_latestPromotionId = _nextPromotionId;

This calculation can be done much more efficiently as follows:

uint256 _nextPromotionId = ++_latestPromotionId;

Incrementing is cheaper than applying + 1 and this way less loads are required.

[PierrickGT]

It may be more gas efficient but it is also less legible, so for this reason, we won't implement this change.

[dmvt]

This is a gas optimization, not a non-critical.