attrdict package currently incompatible with Python 3.10

[johnsekar]

Python 3.10 moves container ABCs (Mapping, etc.) to collections.abc module, which breaks older unmaintained packages like attrdict.

Alternatives:

1. Fork of attrdict, which updates the import statements (https://github.com/johnsekar/AttrDict)
2. Use types.SimpleNamespace from the standard library.

As far as I can tell, the only module affected in wc_utils is wc_utils/util/chem/core.py