fix: Adds autoload support for external libraries

Integrates Composer's autoloading to streamline library
inclusion, facilitating easier extension and maintenance of
dependencies such as PhpSpreadsheet.

details.php

@@ -7,6 +7,7 @@ require_once($CFG->libdir . '/formslib.php');
 require_once($CFG->dirroot . '/user/selector/lib.php');
 require_once('classes/user_selector.php');
 require_once('classes/usergrades_form.php');
+require_once('vendor/autoload.php');
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PhpOffice\PhpSpreadsheet\Writer\Xlsx;