purpose property

Implementation

@override
Bip44 get purpose {
  if (!isLevel(Bip44Levels.master)) {
    throw Bip44DepthError(
      "Current depth (${bip32.depth.toInt()}) is not suitable for deriving purpose",
    );
  }
  return Bip44._(
    bip32.childKey(coinConf.purpose ?? Bip44Const.purpose),
    coinConf,
  );
}