Fix py_structs import errors across codebase

[kanishkaganguly]

When installing from source using python3 -m pip install ".[interactive]" and trying to run multical -h, there are import errors across multiple files. This is running on Python3.8 inside a virtual environment.

Upon investigation, it would appear to be originating from the py_structs package, which seems to be using a different directory structure than what multical is expecting. This might be due to a change upstream, maybe. This PR fixes all import errors and allows multical -h to run without crashing/errors. Whether calibration actually works is a different issue, and is under testing.