fix: preserve deferred WordPress hook lifecycle

[chubes4]

Summary

• let wordpress.phpunit own WordPress bootstrap instead of preloading the runtime's single-site wp-load.php
• defer external-MySQL multisite setup to the managed WordPress test installer, where network tables and constants are established together
• replay plugin and dependency fallback lifecycle callbacks through an isolated WP_Hook, preserving callbacks registered at later priorities
• retain replayed and dynamically added callbacks without rerunning callbacks WordPress already dispatched
• add disposable external-MySQL integration coverage for real mysqli, JSON_VALID, is_multisite(), switch_to_blog()/restore, lifecycle hooks, and nested priority-0 to priority-15 init replay

Verification

• npm run build
• npx tsx tests/phpunit-project-autoload.test.ts
• npx tsx tests/playground-cli-runner-bootstrap-ini.test.ts
• npm run test:playground-phpunit-readonly-cache-integration
• npm run test:disposable-mysql-mysqli-e2e via Docker-backed contracts check: https://github.com/Automattic/wp-codebox/actions/runs/30067914905/job/89402399263

Closes #2007.

Consumer context: Extra-Chill/data-machine-events#546.

[chubes4]

Consumer verification update from Extra-Chill/data-machine-events#546:\n\n- Added and pushed commit 42f4489, which captures init callbacks when the component is first loaded by the dependency-mount fallback.\n- The real Playground integration now covers multisite plus a priority-0 init callback that registers a priority-15 callback; it passes locally.\n- DME workflow run https://github.com/Extra-Chill/data-machine-events/actions/runs/30066183996 improved from 129 to 104 failures. Block, ability, vendor, REST lifecycle, and canonical venue mutation acceptance now pass.\n- Remaining owner-runtime failure: WordPressLifecycleTest::test_runtime_provides_multisite_blog_switching still sees is_multisite() === false in the external-MySQL GitHub Actions runtime, despite HOMEBOY_WORDPRESS_MULTISITE=1. The SQLite Playground integration on this branch sees multisite correctly, so the residual is specific to the external-MySQL runtime path/configuration handoff.\n\nDME remains blocked from final PR until that MySQL multisite path is faithful.