Refactor isActive field to be a helper function instead or rely only on closeDay

[vm06007]

wise-token-contracts/contracts/Declaration.sol

Lines 170 to 182 in fe975b5

	struct Stake {
	uint256 stakesShares;
	uint256 stakedAmount;
	uint256 rewardAmount;
	uint64 startDay;
	uint64 lockDays;
	uint64 finalDay;
	uint64 closeDay;
	uint256 scrapeDay;
	uint256 daiEquivalent;
	uint256 referrerShares;
	address referrer;
	bool isActive;

it is possible to refactor or get rid of one of the fields in the Stake structure, as isActive can be determined by closeDay

zero - active
non zero - inactive

with that it is possible either add a helper function _isActive(stake.closeDay) to determine if the stake is active or not or completely remove this field and rely only on closeDay field. This is not a bug, just an improvement/refactoring in general to avoid extra fields and for better optimization. (only if time allows)