Scanning states for the media events timeline screen

[Velin92]

This PR adds a scanning and a failure state for the elements of the MediaEventsTimeline, precisely for images and videos (since files audio and voice messages, will reuse the existing implementation). Here however it needs to be pointed out that for files, audio, images and videos in these views, we are for now allowing the tap actions, and the reason is that this opens up a scrollable preview of the elements, which in turn will display an error state when an unsafe file is displayed (so the download prevention is still happening, and we have an extra error state view in the preview), so that it's still possible to swipe between the elements in order, but prevent the download of such elements. However this last bit of the feature will be implemented in the next PR. Will however double check with design if we intend to prevent the tap altogether or not

[pixlwave]

LGTM!

[codecov]

Codecov Report

❌ Patch coverage is 95.94595% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.28%. Comparing base (9e1d95d) to head (b943344).
⚠️ Report is 2 commits behind head on develop.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...w/TimelineViews/VideoMediaEventsTimelineView.swift	78.57%	3 Missing ⚠️
...imelineScreen/View/MediaEventsTimelineScreen.swift	96.77%	2 Missing ⚠️
...r/TestablePreview/TestablePreviewsDictionary.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5847      +/-   ##
===========================================
+ Coverage    74.23%   74.28%   +0.04%     
===========================================
  Files          818      819       +1     
  Lines        57284    57407     +123     
===========================================
+ Hits         42525    42642     +117     
- Misses       14759    14765       +6     

Flag	Coverage Δ
unittests	64.52% <95.94%> (+0.06%)	⬆️

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