Function eip191_hash_message

pub fn eip191_hash_message<T>(message: T) -> FixedBytes<32>
where
    T: AsRef<[u8]>,

Hash a message according to EIP-191 (version 0x01).

The final message is a UTF-8 string, encoded as follows: "\x19Ethereum Signed Message:\n" + message.length + message

This message is then hashed using Keccak-256.