fix(perf): back out commit 808b951

This backs out comit 808b951
"Remove optimization which gives worst benchmark results", as it
severely degrades performances as shown in
<#639>.

Author: samueltardieu

src/directed/dijkstra.rs

@@ -214,11 +214,17 @@ where
     let mut target_reached = None;
     while let Some(SmallestHolder { cost, index }) = to_see.pop() {
         let successors = {
-            let (node, _) = parents.get_index(index).unwrap();
+            let (node, &(_, c)) = parents.get_index(index).unwrap();
             if stop(node) {
                 target_reached = Some(index);
                 break;
             }
+            // We may have inserted a node several time into the binary heap if we found
+            // a better way to access it. Ensure that we are currently dealing with the
+            // best path and discard the others.
+            if cost > c {
+                continue;
+            }
             successors(node)
         };
         for (successor, move_cost) in successors {