Hello,
Well, one solution would be to add that line
namespace hikaserial\lib\phpQRCode;
At the very beginning of every file in the "inc/phpqrcode/" folder.
Then in the "inc/qrcode.php" file use
if(!class_exists('hikaserial\lib\phpQRCode\QRencode'))
And
$this->factory = hikaserial\lib\phpQRCode\QRencode::factory($level, $pixelPerPoint, $outerFrame);
To right use the namespace for the checks.
And I think it should avoid your issue.
For what I could see, there is no special usage of external classes in the lib PHPQRCode so, it should not require extra modification to handle the root namespace (but I can't be entirely sure without a lot of tests).
Regards,