stdpar Tutorial: Change iterator_category of cartesian product view iterators to random access. This fixes the major performance bug where thrust::distance/cuda::std::distance will be O(N) for cartesian product views.

Author: brycelelbach

stdpar-tutorial/include/ranges

@@ -9588,7 +9588,7 @@ namespace views::__adaptor
     friend cartesian_product_view;
 
   public:
-    using iterator_category = input_iterator_tag;
+    using iterator_category = random_access_iterator_tag;
     using iterator_concept = decltype(_S_iter_concept());
     using value_type
       = __detail::__tuple_or_pair_t<range_value_t<__maybe_const_t<_Const, _First>>,