Revert "remove tox dependencies"

[thorbjoernl]

• Reverts remove tox dependencies #1475
• Adds comment to make the purposed of this dependency list clear.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.47%. Comparing base (4b2a3fa) to head (8e7d4d1).
Report is 4 commits behind head on main-dev.

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1483   +/-   ##
=========================================
  Coverage     78.47%   78.47%           
=========================================
  Files           139      139           
  Lines         21136    21136           
=========================================
  Hits          16587    16587           
  Misses         4549     4549           

Flag	Coverage Δ
unittests	78.47% <ø> (ø)

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