[WIP] Memory usage and timeout issues with latest version

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Describe the bug Many users are reporting issues due to memory usage and max_execution_time. The backup runs successfully after a refresh but is not as smooth as before. This mainly affects scheduled backups as they never completes.

To Reproduce Steps to reproduce the behavior: No clear steps to replicate. Backup are processed after a refresh.

Expected behavior Backup should work normally without refreshing.

Related threads/tickets https://wordpress.org/support/topic/sometimes-backup-gets-stuck/#post-17882635 (WP Optimize) https://wordpress.org/support/topic/sometimes-backup-gets-stuck/#post-17878681 (Autoptimize) https://wordpress.org/support/topic/max-execution-time-and-max-allocated-memory-errors/#post-17892047 (4.1.0 works) https://wordpress.org/support/topic/max-execution-time-exceeded-while-listing-folders/ (WP Optimize is installed) https://wordpress.org/support/topic/job-has-started-but-not-responded-for-10-seconds-23/ https://wordpress.org/support/topic/erreur-backup/

Additional context Until now, we have learned that rolling back to the older version 4.1.0 fixes the issue. Also, it seems caching/optimization plugins could be the reason as few users reported conflict with WP Optimize, autooptimize.

Acceptance Criteria (for WP Media team use only) Clear instructions for developers, to be added before the grooming

wp-media / backwpup

[WIP] Memory usage and timeout issues with latest version #139