Use `0x` xor `h` prefix consistenly.

[armfazh]

Use an hex prefix consistenly, either 0x xor h, but not both.

From draft v09

key_dst = h'4242535f424c53313233383147315f584f463a5348414b452d3235365f53
             5357555f524f5f4832475f484d32535f4b455947454e5f4453545f'
SK = 0x'2eee0f60a8a3a8bec0ee942bfd46cbdae9a0738ee68f5a64e7238311cf09
         a079'

[armfazh]

Since scalars are defined as integers, then the 0x prefix is correct.
However, the single quotes are unnecessary.

See hex numeric examples at: https://datatracker.ietf.org/doc/html/rfc8610#appendix-G.5

[BasileiosKal]

Hey @armfazh! Thanks for catching this. It should be fixed in PR #337