_guardEntries can be optimized

[St4rgarden]

The humble reentrancy guard built into HSG is the inefficient and older way to implement re-entrancy guard.

Each time the guard is set to a value of 1 from zero it requires a full 20_000 SSTORE call; and refunds 19_900 gas when decremented.

Changing a previously initialized value from 1 to 2 and back to 1 can be significantly more efficient; depending on how much of a transaction's refund can be utilized. In the case of calling a function that relies on applying it's own refund mechanism - the cap can be hit and the refund from "deleting" the _guardEntries variable will not be applied.

Changing the value from 1 to 2 only costs 2900 gas - and refunds 2800 when decremented.