Privacy: Schedule _wp_personal_data_cleanup_requests() on WP-Cron and fix timezone bug in expiry query

[masteradhoc]

Trac ticket: https://core.trac.wordpress.org/ticket/44498

What

Adds a WP-Cron schedule for _wp_personal_data_cleanup_requests() so
that expired, unconfirmed privacy requests are cleaned up automatically
— not only when an admin visits the Export or Erase Personal Data pages.

Also fixes a pre-existing timezone bug in the expiry query that caused
requests to fail immediately on sites in UTC+ timezones.

Changes

wp-includes/functions.php

• wp_schedule_personal_data_cleanup_requests() — registers an hourly
  cron event, matching the pattern of
  wp_schedule_delete_old_privacy_export_files().
• wp_cron_personal_data_cleanup_requests() — cron callback that
  requires wp-admin/includes/privacy-tools.php before calling
  _wp_personal_data_cleanup_requests(), since that file is not loaded
  in a cron request context.

wp-includes/default-filters.php

• Hooks both new functions into init and the cron event, following
  the same pattern as the existing export-file cleanup hooks.

wp-admin/includes/privacy-tools.php

• Changes the date_query column from post_modified_gmt to
  post_modified. WP_Date_Query::build_mysql_datetime() resolves
  relative strings like "86400 seconds ago" using the site's local
  timezone and returns a local-time string. Comparing that against
  post_modified_gmt (UTC) produced the wrong threshold for any site
  not on UTC — immediate failure on UTC+ sites, over-long expiry on
  UTC- sites. Using post_modified (local time) makes both sides of
  the comparison consistent.

Backward compatibility

The direct calls to _wp_personal_data_cleanup_requests() in
export-personal-data.php and erase-personal-data.php are unchanged
and continue to serve as a synchronous fallback on admin page visits.

Trac ticket: https://core.trac.wordpress.org/ticket/44498

Use of AI Tools

AI assistance: Yes
Tool(s): Claude
Model(s): Sonnet 4.6
Used for: Code review and manual test suggestions to test extensively; final implementation were reviewed and fully tested by me.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

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[mukeshpanchal27]

What is intention for running the cron every hours?