allow len without is_empty

src/osu/mod.rs

@@ -219,6 +219,7 @@ pub struct OsuStrains {
 impl OsuStrains {
     /// Returns the number of strain peaks per skill.
     #[inline]
+    #[allow(clippy::len_without_is_empty)]
     pub fn len(&self) -> usize {
         self.aim.len()
     }