You should use the new package, it has a new name nanodart
Low-level functions for NANO/BANANO written in DART. Similar structure to jnano-commons for Java
Examples:
# Generate a random seed
String randomSeed = NanoSeeds.generateSeed();
# Validate a seed
bool seedIsValid = NanoSeeds.isValid(randomSeed);
# Create private key from seed at index 0
String privateKey = NanoKeys.seedToPrivate(seed, 0);
# Create public key from private key
String publicKey = NanoKeys.createPublicKey(privateKey);
# Create account from public get (nano_/ban_ address)
String address = NanoAccounts.createAccount(NanoAccountType.NANO, publicKey);
# Compute state block hash
computeStateHash(int accountType, String account, String previous, String representative, BigInt balance, String link);
# Sign a block
NanoSignatures.signBlock(hash, privateKey);