test: Convert from Mockito to Mockk and Assertj to assertk

[kingargyle]

This will update the kotlin tests to use mockk and assertk. All tests will eventually be updated.

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 12 lines in your changes missing coverage. Please review.

Project coverage is 38.99%. Comparing base (2aef511) to head (9e4c601).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...lds/serenity/ui/video/player/ExoplayerPresenter.kt	57.14%	6 Missing ⚠️
...lds/serenity/ui/video/player/PlaybackRepository.kt	66.66%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #460      +/-   ##
=============================================
+ Coverage      38.86%   38.99%   +0.12%     
- Complexity       272      273       +1     
=============================================
  Files             37       37              
  Lines           1572     1590      +18     
  Branches         156      157       +1     
=============================================
+ Hits             611      620       +9     
- Misses           926      932       +6     
- Partials          35       38       +3     

Flag	Coverage Δ
unittests	38.99% <62.50%> (+0.12%)	⬆️

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud