plans for async implementation of libxduauth

[Blindinlights]

I'm using libxduauth and noticed that currently it only provides synchronous APIs. Considering many applications are moving towards async programming, I'm wondering if there are any plans to implement async interfaces for libxduauth in the future.

I have written this async implementation at this. If you think it's helpful, I can also submit PR.

[frankli0324]

a PR would be nice. please control how large the diff is.