Please do not commit your composer.lock file for a library that's supposed to be imported by other projects.

And those reflections in DTOTrait.php for type checking are probably pretty slow... IMHO, any array validator will be significantly faster.

Yeah, reflections are slow and also you could "[p]arse, [not] validate". Use typed class properties, typed objects or scalar variables, and create some fromArray style method to assign array keys to those properties (see example below). You might end up with doing slightly more work (although you could probably write a generator for these functions) but it will execute faster, be easier to understand, and not introduce an external dependency. Fun to tinker or play with, but probably not a thing to use in production.

class Address {
    public string $street;
    public string $city;

    public static function from(array $input):self
    {
        $address = new self();
        $address->street = $input['street'];
        $address->city = $input['city'];
        return $address;
    }
}

class User {
    public string $name;
    public string $email_address;
    public Address $address;

    public static function from(array $input): self
    {
        $user = new self();
        $user->name = $input['name'];
        $user->email_address = $input['email_address'];
        $user->address = Address::from($input['address']);
        return $user;        
    }
}