Converting underlying DAG implementation to use vectors for storage

Reduces hashing required and speeds up traversals

tests/unit_dag.cpp

@@ -63,7 +63,9 @@ TEST_CASE("dag_traversal", "[dag]")
     std::vector<size_t> visitOrder(N_VERTICES);
     size_t i = 0;
     while (!dag.allVisited()) {
-      const auto v = dag.visitNext().value();
+      auto o = dag.visitNext();
+      REQUIRE(o.has_value());
+      const auto v = o.value();
       dag.completeVisit(v.first);
       visitOrder[v.first] = i;
       ++i;