sign method
Implementation
@override
void sign() {
final message = txData.solanaTransaction.message;
final Uint8List serializedMessage = message.serialize().asUint8List();
txData.message = dynamicToString(serializedMessage);
txData.signature = wallet.sign(txData.message);
txData.isSigned = true;
txData.solanaTransaction.signatures[0] = txData.signature.toUint8List();
}