createNullifier string message throws

[yunus433]

Create nullifier function supports only BigInt convertable strings, can you please add support for regular strings through converting the string to a BigInt inside the createNullifier function. Thank you.

This is important as the user cannot check what are they creating the nullifier for from a BigInt if we do the conversion before sending it to the wallet.

[lvshaoping007]

I'll take a look at this and leave a comment here if there's any further progress.