Share one recursive delete and validate hashes before deleting

[erseco]

Stacked on #140.

One recursive delete, and hash-validated deletes

• Shared delete helper:
  • The upload handler and the reprocessor each had a private copy of the recursive delete that ExeLearning_Styles_Service already exposes publicly. They now call that one.
  • It stops on an unreadable directory instead of passing scandir()'s false to array_diff(), which is a TypeError on PHP 8.
• Hash validation:
  • Problem: exelearning_delete_extracted_folder() (on delete_attachment) and ExeLearning_Reprocessor::cleanup_by_hash() deleted whatever folder the stored value or argument named. A _exelearning_extracted value of .. resolved to uploads/ itself.
  • Fix: both now act only on a well-formed 40-character hash (ExeLearning_Content_Hash_Aliases::is_valid_hash()), which is all the plugin ever writes.

The REST controller's own copy is removed with the rest of its dead code in the next PR.

Tests

• New test: a malformed hash (..) never deletes the extraction root.
• Tests that reflected on the removed private method were dropped.
• Full suite: OK (950 tests).

[github-actions]

Test in WordPress Playground

Test the plugin with the code from this branch:

ℹ️ The eXeLearning editor is fetched from the shared release and unpacked into the plugin when the playground boots, so the first load may take a few extra seconds. ELP upload, shortcode, Gutenberg block and preview work normally.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.86%. Comparing base (0fd11b7) to head (93abef9).

Files with missing lines	Patch %	Lines
includes/class-styles-service.php	75.00%	1 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                      @@
##             feature/make-up-offline     #141      +/-   ##
=============================================================
- Coverage                      96.87%   96.86%   -0.02%     
+ Complexity                       864      855       -9     
=============================================================
  Files                             39       39              
  Lines                           4324     4308      -16     
=============================================================
- Hits                            4189     4173      -16     
  Misses                           135      135              

Flag	Coverage Δ
javascript	95.71% <ø> (ø)
php	97.23% <88.88%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
includes/class-elp-reprocessor.php	99.36% <100.00%> (+0.56%)	⬆️
includes/class-elp-upload-handler.php	100.00% <100.00%> (ø)
includes/class-styles-service.php	96.34% <75.00%> (-0.38%)	⬇️

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