[josbeir]

This updates the plugin for CakePHP 6 on PHP 8.5, dropping CakePHP 5 support. The PR targets the cake6 branch.

• Require CakePHP ^6.0, PHP >=8.5, and PHPUnit ^13.0. Allow development dependencies with stable versions preferred while CakePHP 6 and Chronos 4 are unreleased.
• Rename configuration properties and protected members to follow CakePHP 6 conventions. The configuration rename fixes middleware initialization and missing helper defaults.
• Update failure-event examples and tests to use $event->setResult($response), and restore parent test setup for state isolation.
• Run CI on PHP 8.5 with Glide 3 and 4, CakePHP 6 coding standards, PHPStan, and Psalm. Document the requirements and subclass migration.

Validation: PHP 8.5.12, CakePHP 6.x-dev at d5d303d, PHPUnit 13.4.5. All 19 tests / 42 assertions pass with both Glide 3.2.0 and 4.2.0 using --display-all-issues --fail-on-all-issues. PHPCS, PHPStan level 8, Psalm, composer validate --strict, and git diff --check pass.

Upgrade-tool validation: ran the local cakephp/upgrade checkout at 7a0d340 with Rector 2.6.7 and the cakephp60 ruleset in dry-run mode over src and tests. No further changes were suggested on this branch. Also checked the original source with CakePHP 5.4.3 dependencies: the tool suggested the helper default-configuration property rename, already included here.