docs: define module level docstrings

[Snipy7374]

Change Summary

• Closes Add module docstrings #272 defining module level dosctrings

Hi, my wording isn't that great so if someone wants to suggests changes it would be much appreciated.
Furthermore i haven't defined docstrings for

• builder.py.jinja
• fields.py.jinja
• partials.py.jinja

because i'm unsure how to describe them. Additionally i was wondering if we could use examples (in docstrings) where possible and (maybe) generate them dinamycally (using jinja funtionalities) based on models etc...

Checklist

• Unit tests for the changes exist
• Tests pass without significant drop in coverage
• Documentation reflects changes where applicable
• Test snapshots have been updated if applicable

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