verify method
Implementation
Future<bool> verify() async {
_verifyCertTime();
final rootHash = await reconstruct(cert.tree);
final derKey = await _checkDelegation(cert.delegation);
final key = extractDER(derKey);
final sig = cert.signature;
final msg = u8aConcat([domainSep('ic-state-root'), rootHash]);
final res = await _bls.blsVerify(key, sig, msg);
verified = res;
return res;
}