fix(utxo-lib): pass buffer to `hash256`
fix(utxo-lib): pass buffer to `hash256`

The `utxolib.crypto.*` are essentially wrappers around nodes
`crypto.createHash` interface.

Strings are converted to buffers with `utf8` encoding by default.

Issue: BG-32852

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS