feat(mapper): allow mapping value to object via cast method

[Jeroen-G]

This PR allows the following code:

$data = ['name' => 'Jeroen', 'updated' => new DateTime('now')];
$user = map($data)->to(User::class);

final class User
{
    public function __construct(
        public Name $name,
        public DateTime $updated,
    ){}
}

final class Name
{
    private function __construct(
        private string $name,
    )
    {}

    public static function cast(mixed $value): self
    {
        return new self((string) $value);
    }
}

So what is now possible is the mapping of any data, also nested within arrays, to be mapped to objects without having to create a CastWith caster for each of them. For me this removes the papercut that for every (small) value object I had to create a corresponding caster.

[Jeroen-G]

I don't see how all those tests fail due to these changes 🤨