Minor version of Yii Arrays package is released.

• Change PHP constraint in composer.json to ~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0
• Improve psalm types in ArrayHelper::getObjectVars(), ArrayableInterface, ArrayableTrait and ArrayAccessTrait
• Raise the minimum PHP version to 8.1
• Explicitly mark nullable parameters
• ArrayHelper::getValue() returns default value on empty array key
• ArrayHelper::keyExists() returns false on empty array key