Upgrade test tooling to Pest 5

[howdu]

Summary

• upgrade Core to PHP 8.4, Pest 5, PHPUnit 13, and the first-party Pest PHPStan plugin
• resolve the first-party plugin migration findings
• remove the obsolete Pest 4 shard vendor patch
• make direct Pest shard discovery compatible with Pest 5 by configuring worker memory in phpunit.xml instead of forwarding ParaTest-only options
• refresh Composer dependencies against the merged PHP 8.4/Pest 5 Blade coverage plugin

Dependency

• Add Pest 5 support pest-plugin-blade-coverage#4 is merged at 0877d51058f2d1cc2b89fe93b3c0566c1d5ca2fd

Verification

• composer update --with-all-dependencies --no-interaction
• exact test:fast:ci shard 2/3 reproducer: 1 test, 31 assertions
• FullTestWorkflowDatabaseIsolationTest: 1 test, 31 assertions
• full serial Pest: 3,720 tests, 17,927 assertions
• composer phpstan: 0 errors
• Rector clean
• Pint and diff checks clean

No publication, tag, deployment, migration, staging, or production mutation is included.