Performance improvements and fix warnings

src/priority_queue/fibonacci_heap.rs

@@ -81,7 +81,7 @@ where
         }
     }
 
-    fn decrease_key(&mut self, handle: &Self::Handle, f: impl Fn(&mut T)) {
+    fn decrease_key(&mut self, _handle: &Self::Handle, _f: impl Fn(&mut T)) {
         todo!()
     }
 }
@@ -127,7 +127,7 @@ where
         }
 
         let mut prev = None;
-        let mut start = None;
+        // let mut start = None;
 
         for h in &mut self.update_rank {
             if let Some(h) = h.take() {
@@ -136,7 +136,7 @@ where
                     self.arena.get_mut(&p).right = h;
                 } else {
                     prev = Some(h);
-                    start = Some(h);
+                    // start = Some(h);
                 }
                 if let Some(m) = self.min {
                     if self.arena.get(&h).data < self.arena.get(&m).data {