sequence: relax iterate to support ranges::input_range

Author: petertran858

include/exec/sequence/iterate.hpp

@@ -162,7 +162,7 @@ namespace exec {
     };
 
     struct iterate_t {
-      template <std::ranges::forward_range _Range>
+      template <std::ranges::input_range _Range>
         requires __decay_copyable<_Range>
       auto operator()(_Range&& __range) const {
         return make_sequence_expr<iterate_t>(__decay_t<_Range>{static_cast<_Range&&>(__range)});