fix(uninstall): remove two_factor_enabled_providers option on uninstall

[faisalahammad]

Summary

The two_factor_enabled_providers option (added in 0.16) was not being removed when the plugin is uninstalled, leaving an orphaned row in wp_options. This fix adds the option to the uninstall list and centralises the key in a class constant.

Fixes #902

Changes

class-two-factor-core.php

Before:

$option_keys = array();

After:

const ENABLED_PROVIDERS_OPTION_KEY = 'two_factor_enabled_providers';

// ...

// Keep this updated as plugin-level options are added or removed.
$option_keys = array(
    self::ENABLED_PROVIDERS_OPTION_KEY,
);

Why: Mirrors the existing pattern of constants-on-the-class for every other plugin meta/option key and adds the missing option to the uninstall list.

two-factor.php and settings/class-two-factor-settings.php

Replaced the literal 'two_factor_enabled_providers' with Two_Factor_Core::ENABLED_PROVIDERS_OPTION_KEY so the key lives in one place.

tests/class-two-factor-core.php

Added test_uninstall_removes_enabled_providers_option to cover the new cleanup path.

Testing

Test 1: Automated

1. npm test
2. Filter to uninstall: npm run composer -- test -- --filter test_uninstall

Result: 185/185 pass (6 uninstall tests pass, including the new one).

Test 2: Manual

1. WP Admin → Settings → Two-Factor, save a non-default provider set.
2. WP Admin → Plugins → Deactivate then Delete "Two Factor".
3. Inspect wp_options: no two_factor_enabled_providers row.
4. Reinstall the plugin: settings page loads, "never saved" default applies.

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Co-authored-by: faisalahammad <faisalahammad@git.wordpress.org>
Co-authored-by: kasparsd <kasparsd@git.wordpress.org>
Co-authored-by: masteradhoc <masteradhoc@git.wordpress.org>

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[kasparsd]

Nice, looks great!

[faisalahammad]

Done. Removed TESTING_INSTRUCTIONS.md from the PR (was a manual testing artifact left in the tree by mistake). Amended onto the existing commit, force-pushed to fix/902-uninstall-option-cleanup.

Diff: https://github.com/WordPress/two-factor/pull/903/files