scrypt: allow hash.Hash payload, similar to hkdf & pbkdf2

[paepckehh]

Allow to adapt payload type & complexity via hash.Hash Interface, similar to all other golang.org/x/crypto KDF functions (hkdf, pbkdf2,...).

This would allow to continue to use and apapt existing scrypt based implementations in 2023+, ignoring the increased (cheap) availibility of sha2 hardware assisted solutions.

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