Migrated the SettingsScreen to use datastore instead of SharedPreferences.

[MohitMaliFtechiz]

Fixes #4515

Parent PR #4514.

Continuing from #4514

• Migrated the BackToTop functionality to use dataStore.
• Migrated the OpenInNewTab functionality to use dataStore.
• Migrated the ExternalLinkPopup functionality to use dataStore.
• Refactored the ExternalLinkOpenerTest according to dataStore.
• Migrated the PrefWifiOnly functionality to use dataStore.
• Migrated the Theme functionality to use dataStore.
• Refactored the ThemeConfigTest.
• Refactored the UI test cases to use KiwixDataStore instead of SharedPreferences.
• Added SharedPreferenceToDatastoreMigratorTest to properly verify the migration process.

[codecov]

Codecov Report

❌ Patch coverage is 63.75546% with 83 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.79%. Comparing base (0b14cf6) to head (6fbce77).

Files with missing lines	Patch %	Lines
...estination/library/online/OnlineLibraryFragment.kt	20.83%	15 Missing and 4 partials ⚠️
...kiwixmobile/core/utils/datastore/KiwixDataStore.kt	64.70%	11 Missing and 7 partials ⚠️
...kiwixmobile/core/main/reader/CoreReaderFragment.kt	29.41%	3 Missing and 9 partials ⚠️
...kiwix/kiwixmobile/core/utils/ExternalLinkOpener.kt	10.00%	9 Missing ⚠️
...rg/kiwix/kiwixmobile/core/main/CoreMainActivity.kt	0.00%	6 Missing ⚠️
.../kiwixmobile/core/settings/CoreSettingsFragment.kt	20.00%	2 Missing and 2 partials ⚠️
...wix/kiwixmobile/core/settings/SettingsPresenter.kt	42.85%	4 Missing ⚠️
.../kiwixmobile/core/extensions/FragmentExtensions.kt	50.00%	1 Missing and 2 partials ⚠️
...obile/core/settings/viewmodel/SettingsViewModel.kt	93.33%	3 Missing ⚠️
...loader/downloadManager/DownloadManagerRequester.kt	60.00%	0 Missing and 2 partials ⚠️
... and 3 more

❌ Your patch check has failed because the patch coverage (63.75%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4516      +/-   ##
============================================
- Coverage     58.96%   58.79%   -0.17%     
- Complexity     1520     1527       +7     
============================================
  Files           324      327       +3     
  Lines         17500    17627     +127     
  Branches       2179     2185       +6     
============================================
+ Hits          10318    10364      +46     
- Misses         5757     5834      +77     
- Partials       1425     1429       +4     

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