Refactor karateclub dependency

[ffl096]

Unfortunately we cannot have a direct source dependency when packaging for PyPI, which we need for a more up-to-date karateclub (see #49).
Lets use a "standard" dependency on karateclub for now and ask the user to manually install the source version.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.61%. Comparing base (3d82209) to head (eddf08c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #58   +/-   ##
=======================================
  Coverage   96.61%   96.61%           
=======================================
  Files           8        8           
  Lines         177      177           
=======================================
  Hits          171      171           
  Misses          6        6           

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