fix(core): use rglob to guess local Python modules

[mkniewallner]

Resolves #740.

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added or modified a feature, documentation in docs is updated

Description of changes

deptry doesn't play well with cases where Python packages use PEP 420 and do not have any Python file in the top directory, like shown in the linked issue. I've added a test case that, without the 2nd commit, fails. Using rglob instead of glob for determining if a directory is a Python package ensures that we recursively search directories, instead of stopping at the first level.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.8%. Comparing base (9ffb0eb) to head (acefa49).

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #753   +/-   ##
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  Coverage   92.8%   92.8%           
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  Files         35      35           
  Lines        920     920           
  Branches     165     165           
=====================================
  Hits         854     854           
  Misses        52      52           
  Partials      14      14           

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