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.

hercules_rt/build.rs

+#![feature(exit_status_error)]
+
 use std::env::var;
 use std::path::Path;
 use std::process::Command;
@@ -9,12 +11,16 @@ fn main() {
             .args(&["src/rtdefs.cu", "-c", "-o"])
             .arg(&format!("{}/rtdefs.o", out_dir))
             .status()
-            .expect("PANIC: NVCC failed when building runtime. Is NVCC installed?");
+            .expect("PANIC: NVCC failed when building runtime. Is NVCC installed?")
+            .exit_ok()
+            .expect("NVCC did not succeed");
         Command::new("ar")
             .current_dir(&Path::new(&out_dir))
             .args(&["crus", "librtdefs.a", "rtdefs.o"])
             .status()
-            .unwrap();
+            .unwrap()
+            .exit_ok()
+            .expect("ar did not succeed");
 
         println!("cargo::rustc-link-search=native={}", out_dir);
         println!("cargo::rustc-link-search=native=/usr/lib/x86_64-linux-gnu/");