python: Replace the image crate with png We weren’t using any of its features anyway, so the png crate is exactly what we need, without the many heavy dependencies of image. https://github.com/image-rs/image-png/pull/670 will eventually make it even faster to build.

//! Module containing a bunch of helper modules.

pub mod bitstream;
pub mod lzss;
pub mod math;
pub mod prng;