I need to install this with python 3.10 because the parent tool requires it. What could be the cause of this?

fastchunking 0.0.3 has no support for Python 3.10. It was released long before Python 3.10. However, it currently supports Python :: 3.5 which is way too old.

What parent package requires it as a dependency? You may consider using a maintained package with similar functionality.