Update integration tests to check content in ZIM

[dan-niles]

Close #253

• Update test_zim_scraper to check more metadata of the ZIM
• Add test_zim_channel_json to check contents of channel.json
• Add test_zim_videos to check existence of video json files, video files, video thumbnails and subtitles.
• Add test_zim_playlists to check existence of playlists json files

[codecov[bot]]

Codecov Report

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

Project coverage is 1.54%. Comparing base (1ba45c3) to head (0fcb9b3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #268 +/- ## ===================================== Coverage 1.54% 1.54% ===================================== Files 11 11 Lines 1102 1102 Branches 162 162 ===================================== Hits 17 17 Misses 1085 1085 ```

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