Use wp_update_image_subsizes() for --only-missing on WP 5.3+

[Copilot]

• Investigate wp_update_image_subsizes() and wp_get_missing_image_subsizes() WP 5.3 API
• Update process_regeneration() to use wp_update_image_subsizes() on WP 5.3+ for the --only-missing case
• Handle WP_Error return from wp_update_image_subsizes() — emit warning, log failure, increment $errors
• Keep the legacy wp_generate_attachment_metadata() path as fallback
• Add a @require-wp-5.3 Behat test scenario verifying the new code path
• Run static analysis and code style checks (lint, phpcs, phpstan — all pass)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Perhaps update process_regeneration() to reflect changes in WP 5.3</issue_title>
<issue_description>Just an FYI that from WP 5.3 there are couple of functions to find and generate missing image sub-sizes, and the image meta is saved after each sub-size is generated.

For back-compat wp_generate_attachment_metadata() still returns the whole image meta array after all sub-sizes have been created (if the server doesn't run out of resources), but is not the best way to generate only missing image sub-sizes. See https://core.trac.wordpress.org/ticket/40439 and https://core.trac.wordpress.org/changeset/45538 (testing and suggestions welcome). </issue_description>

Comments on the Issue (you are @copilot in this section)

@schlessera Thanks for the heads-up, @azaozz !

Yes, that looks like it would make everything a bit more streamlined. However, it also means maintaining two separate execution paths for solving the same issue, which might have different results...

I'll have to spend some time looking into this to see how best to support this new functionality.</comment_new>

• Fixes Perhaps update process_regeneration() to reflect changes in WP 5.3 #113

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[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/Media_Command.php	71.42%	4 Missing ⚠️

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[swissspidy]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a valuable optimization for regenerating media thumbnails on WordPress 5.3 and newer. By leveraging the more efficient wp_update_image_subsizes() function for the --only-missing flag, it avoids unnecessary work and improves reliability through incremental metadata saving. The implementation is solid and is well-supported by a new Behat test case. My feedback includes a minor suggestion to enhance code consistency.