[8.x] Adds parameter casting for cursor paginated items

[jspekken]

This fixes the problem when the primary-key (or other attributes) are
objects (e.g.: value-objects) and can be cast to a string using the
__toString method.

Before, the CursorPaginator would always return a pointer to the current
page instead of the next page because the parameter, which was an
object, could not be converted.

[GrahamCampbell]

I don't think we support doing that? You should use primitives for primary key values.

[jspekken]

Why am I limited to primitives? I'd like to make extensive use of value-objects and use attribute casting to facilitate that:

final class PrimaryKeyAttributeCast implements CastsAttributes
{
    public function get($model, string $key, $value, array $attributes): PrimaryKey
    {
        if ($value === null) {
            return PrimaryKey::generate();
        }

        return PrimaryKey::fromString($value);
    }

    public function set($model, string $key, $value, array $attributes): string
    {
        Assert::isInstanceOf($value, PrimaryKey::class);

        return $value->toString();
    }
}

final class PrimaryKey implements Stringable
{
    private Ulid $value;

    public function __toString(): string
    {
        return $this->toString();
    }
    
    public function toString(): string
    {
        return (string) $this->value;
    }

    public function equals(mixed $other): bool
    {
        if ($other instanceof self && get_class($other) === self::class) {
            return (string) $this->value === (string) $other->value;
        }

        return false;
    }
    
    public static function fromString(string $value): self
    {
        return new self(Ulid::fromString($value, lowercase: false));
    }

    public static function generate(): self
    {
        return new self(Ulid::generate(lowercase: false));
    }

    private function __construct(Ulid $value)
    {
        $this->value = $value;
    }
}

That way I'm able to do something like this:

$item->id->equals($otherItem->id); 
// or even:
$item->equals($otherItem);

This hides hides the implementation details in the value objects.
This works perfectly except that the cursor paginator won't cast an object to a string. This fixes that issue :)