fix: prevent error on general settings save

[Pranjal1423]

What?

Closes #1048

This PR prevents options.php form validation errors on Settings › General saves by preserving and restoring $GLOBALS['new_allowed_options'] when register_initial_settings() is called inside Settings::register().

Why?

Since 1.2.0 (#856), Settings::register() calls register_initial_settings() when abilities initialize before rest_api_init, ensuring core settings exist in $wp_registered_settings before taking the snapshot for core/read-settings.

However, register_initial_settings() has a side effect: it calls register_setting( 'general', 'admin_email' ), which appends 'admin_email' to $new_allowed_options['general'].

On ordinary admin form POSTs to wp-admin/options.php, WordPress iterates over every allowed option in the group and updates it. Because the Settings › General form posts new_admin_email instead of admin_email, options.php receives null for admin_email. In turn, sanitize_option( 'admin_email', null ) / is_email( null ) triggers PHP deprecation notices (preg_match / strlen parameter null) and an invalid email error notice ("The email address isn't correct"), even though the form is completely valid.

How?

1. In includes/Abilities/Settings/Settings.php, captured $GLOBALS['new_allowed_options'] immediately prior to calling register_initial_settings().
2. Restored $GLOBALS['new_allowed_options'] (and re-linked the legacy alias $GLOBALS['new_whitelist_options']) immediately afterwards. This keeps $wp_registered_settings populated for the Abilities registry without leaking admin_email into form handling.
3. Added an integration test test_register_preserves_new_allowed_options() in tests/Integration/Includes/Abilities/Settings/SettingsTest.php to verify that admin_email is not added to $new_allowed_options['general'] and existing allowed options are preserved.

Use of AI Tools

AI assistance: Yes
Tool(s): Antigravity
Used for: Root-cause debugging, patch implementation, and integration test creation; final implementation and tests were tested and reviewed by me.

Testing Instructions

1. Ensure the Custom Abilities experiment is enabled under Settings › AI › Experiments (or an mu-plugin with add_action( 'admin_init', function() { wp_get_abilities(); } ); is active).
2. Navigate to Settings › General (/wp-admin/options-general.php).
3. Scroll to the bottom and click Save Changes without making modifications.
4. Verify the page reloads cleanly with the green "Settings saved." notice, with no deprecation notices or email validation error banners.
5. Verify the PHPUnit integration tests pass:

   npx wp-env run cli vendor/bin/phpunit -c phpunit.xml.dist tests/Integration/Includes/Abilities/Settings/SettingsTest.php

After Fix

Changelog Entry

Fixed - Prevent options.php validation error when saving general settings with abilities active.

[github-actions]

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Co-authored-by: Pranjal1423 <pranjal4804@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>
Co-authored-by: juanlentino <juanml@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.60%. Comparing base (aae6de2) to head (52d72e7).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #1080   +/-   ##
==========================================
  Coverage      81.59%   81.60%           
  Complexity      3081     3081           
==========================================
  Files            129      129           
  Lines          12281    12283    +2     
==========================================
+ Hits           10021    10023    +2     
  Misses          2260     2260           

Flag	Coverage Δ
unit	81.60% <100.00%> (+<0.01%)	⬆️

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