[`rTexViewer`] Support the PFM HDR format

[AregevDev]

rTexViewer already support the PPM format. PFM is an extension that stores float32s from 0 to 1 instead of 0-255 RGB colors.

Use case: I write ray tracers, a simple HDR format really helps for building something simple.

[raysan5]

@AregevDev most image formats supported by raylib come from stb_image library and unfortunately it does not support PFM format, do you have some minimal loading code? maybe it can be added as an external portable library, like I did with QOI

[AregevDev]

I can surely come up with something. Shouldn't be too hard to encode / decode