addition: Generic instance factory

[remipelhate]

When setting up factories for classes with a non-public default constructor, we have to pick one of the named constructors and add some additional logic to ensure all attributes defined by the factory are properly applied to the created instance. The whole point of testing factories is to eliminate "complex" logic while creating instances, so this felt a bit off.

This PR introduces Craftzing\TestBench\Factories\InstanceFactory which uses reflection to completely bypass constructor limitations while creating instances:

final class UserFactory extends ImmutableFactory
{
    protected function instance(array $attributes): User
    {
        return new InstanceFactory(User::class)->make($attributes);
    }
}