signInputAsync method
Implementation
Future<void> signInputAsync(int index, AsyncSignerCallback signer) async {
final inputSection = _getInputSection(index);
final hashType = _getInputSighashType(inputSection) ?? defaultHashType;
final tx = _buildUnsignedTx();
final witnessUtxo = _findInputKv(
inputSection, PsbtInputEntry.witnessUtxo.keyType);
final digest = _computeDigest(tx, index, hashType, inputSection, witnessUtxo);
final sig = await signer(tx, index, digest, hashType);
_storePartialSig(index, sig, hashType);
}