Crypto: Do Blake2b on message before sign/check of BLS by default

Context

This helps uniformize between the different signature schemes. Also the BLS signature / check algorithm probably benefits (at least it is not detrimental) having smaller signed messages in terms of performance.

This MR is a prerequisite for tz4 accounts (!5444 (merged)) and comes before !6295 (merged).

It depends on !6282 (merged).

Manually testing the MR

make test-unit