Fixed: FIND_IN_PAGE feature only works with first tab page.

[MohitMaliFtechiz]

Fixes #4200

• The previously loaded article was not loading in custom apps when switching to another fragment and then returning to the reader screen. Instead, the home page of the ZIM file was loading. A fix has been implemented to resolve this issue.
• Added test cases for custom apps to cover this scenario and prevent future errors.
• Refactored some deprecated methods used in test cases.
• Improved the logic for handling search-related operations to ensure they are performed after tabs are fully restored.
• Previously, the search observation was initiated before the tabs were restored, causing the FIND_IN_PAGE feature to only work in the first tab. This happened because the webView list was empty at the time of observation.
• With the ZIM file opening and tab restoration now moved to background threads, the search observation logic has been moved to after the tabs are restored. This ensures that all webViews are properly initialized before observing search actions.
• This approach is more robust and aligns with the correct lifecycle of tab restoration and search functionality.
• Fixed: The SearchFragmentTestForCustomApp was failing sometimes. See https://github.com/kiwix/kiwix-android/actions/runs/13069386299/job/36467529496

screen-20250131-141856.mp4

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.87%. Comparing base (a6a3843) to head (a9364d5).
Report is 10 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4201      +/-   ##
============================================
- Coverage     56.90%   56.87%   -0.04%     
+ Complexity     1541     1540       -1     
============================================
  Files           313      313              
  Lines         13513    13515       +2     
  Branches       1695     1695              
============================================
- Hits           7690     7687       -3     
- Misses         4654     4659       +5     
  Partials       1169     1169              

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