Fix deprecated implicit nullable parameter warnings in Rabbit Hole module classes and interfaces in PHP 8.4

The Rabbit Hole module (src/ directory) triggers multiple deprecation warnings due to missing explicit nullable types in method signatures.

These occur in various files, including:

src/BehaviorInvoker.php
src/BehaviorInvokerInterface.php
src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php
src/Plugin/RabbitHoleBehaviorPlugin/PageNotFound.php
src/Plugin/RabbitHoleBehaviorPlugin/AccessDenied.php
src/Plugin/RabbitHoleBehaviorPluginBase.php
src/Plugin/RabbitHoleBehaviorPluginInterface.php

Deprecated: Drupal\rabbit_hole\BehaviorInvoker::__construct(): Implicitly marking parameter $module_handler as nullable is deprecated, the explicit nullable type must be used instead in /var/www/docroot/modules/contrib/rabbit_hole/src/BehaviorInvoker.php on line 77

Deprecated: Drupal\rabbit_hole\BehaviorInvoker::processEntity(): Implicitly marking parameter $current_response as nullable is deprecated, the explicit nullable type must be used instead in /var/www/docroot/modules/contrib/rabbit_hole/src/BehaviorInvoker.php on line
125

Deprecated: Drupal\rabbit_hole\BehaviorInvokerInterface::processEntity(): Implicitly marking parameter $current_response as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/BehaviorInvokerInterface.php on line 55

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPlugin\PageRedirect::performAction(): Implicitly marking parameter $current_response as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php on line 117

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPlugin\PageRedirect::settingsForm(): Implicitly marking parameter $entity as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php on line 253

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPlugin\PageRedirect::settingsForm(): Implicitly marking parameter $bundle_settings as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php on line 253

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPluginBase::settingsForm(): Implicitly marking parameter $entity as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPluginBase.php on line 28

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPluginBase::settingsForm(): Implicitly marking parameter $bundle_settings as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPluginBase.php on line 28

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPluginInterface::settingsForm(): Implicitly marking parameter $entity as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPluginInterface.php on line 44

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPluginInterface::settingsForm(): Implicitly marking parameter $bundle_settings as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPluginInterface.php on line 44

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPlugin\PageNotFound::performAction(): Implicitly marking parameter $current_response as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPlugin/PageNotFound.php on line 23

Deprecated: Drupal\rabbit_hole\Plugin\RabbitHoleBehaviorPlugin\AccessDenied::performAction(): Implicitly marking parameter $current_response as nullable is deprecated, the explicit nullable type must be used instead in
/var/www/docroot/modules/contrib/rabbit_hole/src/Plugin/RabbitHoleBehaviorPlugin/AccessDenied.php on line 23