feat: improve Experiment class

[dkrako]

💥 (not really a) Breaking Change

Restricts eyetracker argument to keyword-only. As sampling_rate and eyetracker already was mutually exclusive, I don't see how this would break any existing workflow.

Description

• restricts eyetracker argument to keyword-only
• implements equality operator check Experiment, Screen and EyeTracker for equality #919
• resolves type ambivalence of eyetracker field Avoid type ambivalence in Experiment.screen and Experiment.eyetracker #891
• adds screen argument
• necessary changes to experiment field in DatasetDefinition as Experiment now allows for empty init
• remove irrelevant experiment field from some DatasetDefinitions

This PR now also allows for full equality comparisons between DatasetDefinition instances.

Blocked by #1008

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3a54708) to head (9bb705b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1010   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           78        78           
  Lines         3571      3560   -11     
  Branches       631       629    -2     
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- Hits          3571      3560   -11     

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