There are several changes from the previous iteration:
dims and flatten was replaced with extents, which should fit well
to what the function does and to mdspan::extents().
Some initial inline rst documentation was added, but its not
being build yet.
Header guards were adjusted to the new library name.
#undef NDEBUG was added to testing_common.h to properly
enable assertions in device side testing.

Disable c++17 windows builds because mdspan is not supported there

Also adds a comment describing a new test of rst docs examples

Cleaned up order of annotations and constexpr, removed __device__.
Moved to absolute includes.
Added no discard on all functions in detail namespace
Added c++17 ifdef.
Changed header guards to a new format applicable after I move some files
in a future change.
A couple of _LIBCUDACXX_UNREACHABLE and other fixes

and the main header to hierarchy.cuh

This change adds static_cast to product_type of a given level
on extents operations, instead of the currently only passing it as
extents template argument.
This change also adds a test case for the above issue