style: use sum instead of fold

src/prog.rs

@@ -410,7 +410,7 @@ impl InstRanges {
         self.ranges
             .iter()
             .map(|&(s, e)| 1 + (e as u32) - (s as u32))
-            .fold(0, |acc, len| acc + len) as usize
+            .sum::<u32>() as usize
     }
 }