[Cin] fileexr/fileppm direct copy support

[Andrea paz]

> Please test?
I don't really know what test I could do.
I rendered a video at 120 fps in an OpenEXR image sequence. I loaded
the file in CinGG-appimage (without patches) and the playback goes at
18-23 fps, while moving the cursor up and down the timeline goes in
real time, without freezing or slowing down.
I loaded the same sequence of images into CinGG compiled with the 2
patches and the result is the same: playback at 17-23 fps and
real-time timeline.
I notice no differences
Can you suggest other tests?