fix: utf-8 image filename support

[aonmkugs]

When you attempt to load faces images or paths with special characters you get this kind of errors du to OpenCV's imread not supporting these natively (low chances to get this fixed upstream though):

[ WARN:0@2488.154] global loadsave.cpp:241 cv::findDecoder imread_('C:/B├╝cher\image.jpg'): can't open/read file: check file path/integrit

We can work around this by using np.fromfile which support UTF-8 paths and pass the binary content to OpenCV's imdecode.