perf(physics): the steps of the vehicle physics on many threads, in groups of vehicles which act on one another (performance.cpucores, 0: all cores)

utilities/utilities.h

@@ -62,6 +62,9 @@ inline long Round(double const f)
 
 double Random(double a, double b);
 int Random(int min, int max);
+// the engine Random() draws from in the calling thread, in place of Global.random_engine, or none for that one again. the threads
+// of worker_pool have engines of their own: the one of the simulation can't be shared between threads
+void set_thread_random_engine(std::mt19937 *Engine);
 
 /// @author lxvia
 /// @brief Returns a random seed from the system's entropy source, if available. Otherwise, falls back to a clock-based seed.