Function decrypt_xaes256_gcm 

pub(crate) fn decrypt_xaes256_gcm(
    message: &CoseEncrypt0Bytes,
    key: &XAes256GcmKey,
) -> Result<(Vec<u8>, ContentFormat), CryptoError>

Decrypts a typed COSE Encrypt0 message with an XAES-256-GCM key.