Edge detection

• Juno and rust versions and a harness including verification and the ability to display frames or output the entire videos; we'll probably need to tweak the verification for GPU like with Cava.
• Uses opencv for reading/writing videos and displaying frames. TBH the opencv bindings for Rust are pretty bad, they're pretty close to the C++ ones. I use unsafe in one place to get the frame as a slice.
• Adds an opencv feature, without it edge detection is disabled but it means that we don't have a dependence on having the opencv system package installed (libopencv-dev on Debian/Ubuntu). The feature is enabled for CI, where we run just 2 frames of a video to avoid increasing CI time too much.