Fix default 'before' date in WP-CLI clean command #1343

[MagicGeny]

Description

Closes #1343

This PR fixes an issue where running the wp action-scheduler clean command without specifying the --before flag incorrectly deletes all completed/failed/cancelled actions instead of keeping the last 31 days of data as stated in the documentation.

Cause of the bug

In ActionScheduler_WPCLI_Clean_Command::clean(), the default value for the before argument was set to an empty string ''. When passed further down into strtotime(), this empty string evaluates to "now", causing the cleaner to wipe out even newly created/completed actions.

Solution

Changed the default value from '' to '31 days ago' to align the default CLI behavior with the plugin's default retention period and documentation.

How to test

1. Create some fresh completed actions:
   wp eval 'for($i=0; $i<5; $i++) { $id = as_schedule_single_action(time(), "test", [], "test"); ActionScheduler::store()->mark_complete($id); }'
2. Run the clean command without flags: wp action-scheduler clean
3. Before this fix: All 5 fresh actions are deleted (5 actions deleted.).
4. After this fix: The fresh actions are safely preserved (0 batches processed.).

[MagicGeny]

Hi @barryhughes!

I wanted to provide some context for this PR. This change resolves the default 'before' value issue for the cleanup process.

It is also a crucial dependency for another bugfix I just submitted in #13480 (which addresses the incorrect 'before' filtering in the WP-CLI clean command, #1107).

I have tested this locally, and all tests pass. Please let me know if you would like me to adjust anything here so we can move this forward. Thank you!