Method increment

include/tsutil/Metrics.h:146–152

  }

  int64_t
  increment(IdType id, uint64_t val = 1)
  {
    auto metric = lookup(id);

    return (metric ? metric->_value.fetch_add(val, MEMORY_ORDER) : NOT_FOUND);
  }

  int64_t
  decrement(IdType id, uint64_t val = 1)