Function verify 

pub fn verify(
    alg: DigestAlgorithm,
    pk: &VarLenPublicKey<'_>,
    msg: &[u8],
    salt_len: u32,
    sig: &[u8],
) -> Result<(), Error>

Returns Ok(()) if the provided signature is valid.

Returns an error in any of the following cases:

• the public key is invalid
• the signature verification fails
• the length of msg exceeds u32::MAX
• salt_len exceeds u32::MAX - alg.hash_len() - 8