feat: make all arguments in screen and experiment optional

[josephine-funken]

Description

Removes artificial restriction and allows for all experiment arguments to be None.

Fixes issue #717

Implemented changes

• [x] all Screen attributes are optional
• [x] all Experiment attributes are optional

Type of change

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (bc91b2e) to head (179ca69).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #721 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 60 60 Lines 2757 2801 +44 Branches 709 712 +3 ========================================= + Hits 2757 2801 +44 ```

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