v7.42.0

Redis drop-in lifecycle automation + one-step Save

• Auto-replace the drop-in on plugin update. upgrader_process_complete + an admin_init self-heal bring the deployed wp-content/object-cache.php into line with the bundled version automatically (connection-less, never clobbers a foreign drop-in, only copies when the bundled @version is newer). Previously a version bump only raised a notice the admin had to click — so fixes like v7.41.4 never reached sites until a manual reinstall.
• Auto-(re)install on activation. Covers the WP-Cron update deactivate→reactivate dance leaving a stale/missing drop-in.
• Clean teardown on disable/deactivation. Removes the drop-in and strips the managed Redis block from wp-config.php. Genuine deactivations only — WordPress deactivates silently during updates, so caching survives updates. Saved settings are retained.
• One Save does the lot. Saving Redis settings now also rewrites wp-config.php and refreshes the drop-in when Redis is enabled; enabling writes wp-config.php too. wp-config write skipped when unchanged; backups pruned to the most recent 5.

Includes everything in v7.41.4 (the 4 GB alloptions OOM fix).