write method
Implementation
@override
int write(Uint8List buf) {
buf.buffer.asByteData(buf.offsetInBytes).setInt32(0, 21);
int new_offset = buf.offsetInBytes + 4;
new_offset += FfiConverterString.write(
secp256k1Error, Uint8List.view(buf.buffer, new_offset));
return new_offset;
}