Add <bulk.hpp> to <execution.hpp> (#181)

* fixed how product_type access is done

* clang-format

* added missing bulk.hpp header to execution.hpp

Author: dietmarkuehl

include/beman/execution/execution.hpp

@@ -38,6 +38,7 @@
 #include <beman/execution/detail/connect.hpp>
 #include <beman/execution/detail/schedule.hpp>
 
+#include <beman/execution/detail/bulk.hpp>
 #include <beman/execution/detail/continues_on.hpp>
 #include <beman/execution/detail/into_variant.hpp>
 #include <beman/execution/detail/just.hpp>