Support pivot payload in custom model events

[wimski]

This feature makes the following use case with custom model event classes possible.

class MyModel extends Model
{
    use PivotEventTrait;

    /**
     * @var array<string, class-string>
     */
    protected $dispatchesEvents = [
        'pivotSynced' => MyEvent::class,
    ];
}

readonly class MyEvent
{
    /**
     * @param array{
     *     model: Model,
     *     relation: string,
     *     pivotIds: array<array-key, int|string>,
     *     pivotIdsAttributes: array<int|string, array<string, mixed>>,
     * } $payload
     */
    public function __construct(
        public MyModel $model,
        public array $payload,
    ) {
    }
}

readonly class MyListener
{
    public function __invoke(MyEvent $event): void
    {
         // $event->model
         // $event->payload
    }
}