timers: short-cut timeout extension pattern

in case we constantly extend the same timer the
head might already point to the timer we want
to cancel. in this case we can directly remove the
timer to reduce building up the heap unnecessarily.

src/sources/timer.rs

@@ -229,6 +229,16 @@ impl TimerWheel {
     }
 
     pub(crate) fn cancel(&mut self, counter: u32) {
+        if self
+            .heap
+            .peek()
+            .map(|data| data.counter == counter)
+            .unwrap_or(false)
+        {
+            self.heap.pop();
+            return;
+        };
+
         self.heap
             .iter()
             .find(|data| data.counter == counter)