fix recursion error by adding copy and deepcopy dunder methods

[orionarcher]

Summary

Both copy and deepcopy are currently broken for the InputSet object. This PR implements dunder methods to fix both. There very well may be a more elegant solution but I couldn't find it!

• Feature 1: __copy__ and __deepcopy__ dunder methods

Checklist

• Doc strings have been added in the Google docstring format. Run pydocstyle on your code.
• Type annotations are highly encouraged. Run mypy path/to/file.py to type check your code.
• Tests have been added for any new functionality or bug fixes.
• All linting and tests pass.

[janosh]

Thanks for the fix @orionarcher! 👍