For crypto types, derive ZeroizeOnDrop

[jhand2]

In many places we derive Zeroize for crypto types to satisfy FIPS zeroization requirements. This requires us to manually call .zeroize() on many different values. To prevent forgetting to do this, we should instead derive ZeroizeOnDrop, which will automatically drop types we allocate on the stack.

[sree-revoori1]

The issue is some of the crypto types derive Copy, and we can't derive both ZeroizeOnDrop and Copy since ZeroizeOnDrop uses Drop. So I think we can only do this for types that don't derive Copy.