addition: PHPUnit Eloquent model comparator

[remipelhate]

This PR adds a comparator for PHPUnit's IsEqual assertion to compare Eloquent models. Instead of comparing entire objects, the comparator relies on Eloquents Model::is() method.

To enable the comparator, register it to PHPUnit in the Laravel base test case of your project:

namespace App\Shared\Testing;

use Craftzing\TestBench\Laravel\Constraint\Eloquent\ModelComparator;
use SebastianBergmann\Comparator\Factory;

abstract class TestCase extends IlluminateTestCase
{
    #[Before]
    public function setupConstraints(): void
    {
        Factory::getInstance()->register(new ModelComparator());
    }
}