Unsigned hash object properties

[twoeths]

Motivation This is the way we calculate a HashObject from byte array: https://github.com/ChainSafe/as-sha256/blob/d2b3c07149ba2b590db2d026dc6a45a0e941778b/src/index.js#L92

The result may return negative numbers, we want to make it unsigned integers to be more clean, make sure we don't have any performance impact with that.