Improve permission_callback of Cloudinary Rest API endpoints

[aatanasov-cloudinary]

Fixes #1134 and this topic.

Approach

• Set an appropriate permission_callback to all endpoints created by the plugin.
• The default endpoint now requires the wp_rest nonce.
• Ensured the previously 'permission_callback' => '__return_true' work with the new approach ('permission_callback' => array( 'Cloudinary\REST_API', 'validate_request').
• Only rest_test_rest_api_connectivity uses true (isolated in a separate method) because this is a Rest API check only.

QA notes

• Go to admin.php?page=cloudinary and ensure ui-state and stats AJAX requests resolve.
• Test cron endpoints via code:
  1. Add logs to the daemon_watcher and run_queue methods of class-cron.php
  2. Remove the cloudinary_cron_system and cloudinary_cron_schedule theme options.
  3. Enable cron from page=cloudinary&section=cron_system
  4. Wait for the jobs to start (check the Next Run column)
  5. Check the debug log and ensure there are logs:
  6. Example:

[02-Feb-2026 10:31:59 UTC] Daemon watcher started at 1770028319 with start time 177002831869807d1ea1e06
[02-Feb-2026 10:32:00 UTC] Running cron queue at 1770028320

[gabriel-detassigny]

Everything works as expected 👍