Fix TypeError for AttrDcit in Python <= 3.8

[onpix]

Description of Changes

This PR enhances the AttrDict class in the codebase to support generic types for type hinting. This change is necessary to ensure compatibility with Python 3.8. I noticed that the AttrDict class was being used in a way that suggested it should support subscripting for type hinting (e.g., AttrDict[str, Any]). However, using AttrDict in this way led to a TypeError in Python 3.8:

TypeError: 'type' object is not subscriptable

Code Changes

By adding Generic[K, V] to the AttrDict class, we now ensure compatibility with Python 3.8.