enhancement: add backend to support load data from .py files

[ssato]

Is your feature request related to a problem? Please describe. It may be useful if anyconfig supports load data from .py (python) files.

Describe the solution you'd like Add backend parser to load from .py files, and optionally dump data to .py files.

Describe alternatives you've considered Don't add such feature.

Additional context

Prototype implementations to load data from .py files exist in https://github.com/ssato/python-anyconfig/blob/next/tests/base/utils.py#L32.