add Safety doc in format demanded by clippy

src/utils/wakers/shared_arc.rs

@@ -43,10 +43,10 @@ use std::sync::Arc;
 
 /// A trait to be implemented on [super::WakerArray] and [super::WakerVec] for polymorphism.
 /// These are the type that goes in the Arc. They both contain the Readiness and the redirect array/vec.
+/// # Safety
+/// The `get_redirect_slice` method MUST always return the same slice for the same self.
 pub(super) unsafe trait SharedArcContent {
-    /// Get the reference of the redirect slice. This is used to compute the index.
-    /// This method MUST always return the same slice for the same self.
-    /// Failure to do so may lead to unsafety.
+    /// Get the reference of the redirect slice.
     fn get_redirect_slice(&self) -> &[*const Self];
 
     /// Called when the subfuture at the specified index should be polled.