What is the equiv. of loading system libraries?

Whoever needs this, the following code works

<?php
namespace PHPMaker2025\KOMODO;

use DI\ContainerBuilder;

// Autoload
require_once "../vendor/autoload.php";

// Require files
require_once "../src/constants.php";
require_once "../src/config.php";
require_once "../src/phpfn.php";
require_once "../src/userfn.php";

$containerBuilder = new ContainerBuilder();
$containerBuilder->useAttributes(true);

// Add definitions
$containerBuilder->addDefinitions("../src/definitions.php");

// Dispatch container build event
DispatchEvent(new ContainerBuildEvent($containerBuilder), ContainerBuildEvent::NAME);

// Build PHP-DI container instance
$container = $containerBuilder->build();

$conn = Conn();