deriveKeypair method
Implementation
KeyPair deriveKeypair(String serviceName, {int index = 0}) {
if (services![serviceName] == null) {
throw "Service doesn't exist in the keychain";
}
return deriveArchethicKeypair(
seed, services![serviceName]!.derivationPath!, index,
curve: services![serviceName]!.curve!,);
}