Method reset

tests/async/marl-test/pool_test.cpp:24–27

  CtorDtorCounter() { ctor_count++; }
  ~CtorDtorCounter() { dtor_count++; }
  static void reset() {
    ctor_count = 0;
    dtor_count = 0;
  }
  static int ctor_count;
  static int dtor_count;
};