fix: flaky tests

[kaseyvee]

Changes

• wrap shared viewport tests in a context to avoid double mounting
• reorder and add more test assertions
• compress example video size
• update path of example image

[Shiti]

I've tried running tests with these changes multiple times. It still fails sometimes with the following error

  1) Video
       Mobile and Desktop
         should toggle between fullscreen and normal mode when clicking the fullscreen button on macbook-13 screen:

      AssertionError: expected 200 to equal 1280
      + expected - actual

      -200
      +1280