Avoid type ambivalence in Experiment.screen and Experiment.eyetracker

[saeub]

Current Behavior

At least Experiment.eyetracker can be None (if sampling_rate is passed in Experiment.__init__()). Experiment.screen should always be of type Screen, unless it is tampered with after initialization.

Details: #884 (comment)

Expected Behavior

Experiment.screen should always be of type Screen, Experiment.eyetracker should alwys be of type EyeTracker.

Minimum acceptance criteria

• Implement Experiment.screen and Experiment.eyetracker as non-null properties.

• Remove unnecessary None check in from_asc()

  • see feat: Store metadata from ASC in experiment metadata #884 (comment))
  • resolved in feat: improve Experiment class #1010

• I am running the latest version

• I checked the documentation and found no answer

• I checked to make sure that this issue has not already been filed

• I have provided sufficient information for the team

[dkrako]

I labeled it nonessential as it's only protecting the user against themselves. feel free to raise the priority in case

[dkrako]

I marked #1010 to resolve this issue, as the main issue lies in the type ambivalence of the eyetracker field.

I created #1011 as a followup for making attributes tamper-free.