src: implement ego tracking models, and port shaders from renderbug into here

src/backoff.rs

@@ -56,7 +56,7 @@ impl Backoff {
         'outer: loop {
             for attempt in self.attempts {
                 match &latest {
-                    Err(e) => {
+                    Err(_) => {
                         match attempt {
                             Attempts::Finite(1) => {
                                 warn!("Operation failed on final attempt.");