Gas Optimizations

[code423n4]

Array Optimization

https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L353-L355
i++ can become ++i to save approximately 5 gas per iteration
The part uint i = 0 can become uint i as just letting the default be applied is cheaper than setting i to the default value of 0.
The ++i part can also become unchecked, unchecked{ ++i; } as the createClaimsBatch function will certainly run out of gas before ++i overflows from getting to uint256(-1).

Therefore the new array will be:

for (uint256 i; i < length; ) { 
    _createClaimUnchecked(_recipients[i], _startTimestamps[i], _endTimestamps[i], _cliffReleaseTimestamps[i], _releaseIntervalsSecs[i], 
    _linearVestAmounts[i], _cliffAmounts[i]); 
    unchecked{ ++i; }
}

Using bools for storage incurs unnecessary overhead

Using uint256(1)and uint256(2) for true/false avoids a 100 gas Gwarmaccess, and avoids a 20000 gas Gsset when changing from false to true after having been a true value in the past.

Instances are:
https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L45
https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/AccessProtected.sol#L12

Letting the default of zero be applied to uint variables saves gas

Setting a uint variable to zero costs more than allowing the default value of zero be applied, therefore the = 0 can be removed in these instances:
https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L27
https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L148
(I already mentioned in the array optimization section) https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L353