finish threaded physics implementation

src/state.cpp

@@ -37,6 +37,7 @@ auto StateManager::FillGraph() -> void {
             std::vector<std::pair<std::size_t, std::size_t>>>
       closure = current_state.Closure();
 
+  physics.ClearCmd();
   physics.AddMassSpringsCmd(closure.first.size(), closure.second);
   for (const State &state : closure.first) {
     states.insert(std::make_pair(state, states.size()));