Add type hints and some other tweaks to satisfy PHPStan

lib/CoreFunctions.php

@@ -5,21 +5,24 @@
 use function Safe\ob_end_clean;
 
 // Convenience alias of var_dump.
-function vd($var){
+function vd($var): void{
 	var_dump($var);
 }
 
 // var_dump($var) then die().
-function vdd($var){
+function vdd($var): void{
 	var_dump($var);
 	die();
 }
 
 // var_dump into a string.
-function vds($var){
+function vds($var): string{
 	ob_start();
 	var_dump($var);
 	$str = ob_get_contents();
+	if($str === false){
+		$str = '';
+	}
 	ob_end_clean();
 	return $str;
 }