store masses/springs inside vector and manage unordered_maps for a state<->index mapping

this reduces the time required to iterate over all masses/springs
because data is stored in contiguous memory

src/state.cpp

@@ -84,7 +84,7 @@ auto StateManager::ClearGraph() -> void {
 
 auto StateManager::FindWinningStates() -> void {
   winning_states.clear();
-  for (const auto &[state, mass] : mass_springs.masses) {
+  for (const auto &[state, mass] : mass_springs.state_masses) {
     if (win_conditions[current_preset](state)) {
       winning_states.insert(state);
     }