newSlot method
Attempts to initialize the next slot of the Satscard, revealing a new
public key and making the next slot active. If isUsedUp this will fail.
chainCode
must either be empty (and will be generated by the library) or
a 64-character (32-byte) hex string. spendCode
must be a 6-digit numeric
code
Implementation
Future<Slot> newSlot(Transport transport, String spendCode,
{String chainCode = ""}) =>
Implementation.instance
.satscardNew(transport, spendCode, chainCode, handle)
.then((value) => _sync(value));