A VetKey is in the end a valid BLS signature; this function checks that a
provided BLS signature is the valid one for the provided public key and
message.
When a VetKey struct is created (using EncryptedVetKey.decryptAndVerify) the signature
is already verified, so using this function is only necessary when
using a vetKey as a VRF or for threshold BLS signatures, with the bytes obtained
from VetKey.signatureBytes.
Verify a BLS signature
A VetKey is in the end a valid BLS signature; this function checks that a provided BLS signature is the valid one for the provided public key and message.
When a VetKey struct is created (using EncryptedVetKey.decryptAndVerify) the signature is already verified, so using this function is only necessary when using a vetKey as a VRF or for threshold BLS signatures, with the bytes obtained from VetKey.signatureBytes.