Hex encoding message string breaks verification

[fusion44]

Encoding the message string in hexadecimal before passing it to the bip340 library results in failed verification. On the other hand, direct use of the bip340 library verifies messages successfully.

https://github.com/anasfik/nostr/blob/1ca24ce607d260917e6d06a5f4530c717985dc1d/lib/nostr/instance/keys/keys.dart#L171C1-L172C62.

In order to avoid unnecessary layers of abstraction, I suggest flattening the call stack.