[ENHANCEMENT]: Expose `aow_storage` to the public

[PointKernel]

Is your feature request related to a problem? Please describe.

cuco::experimental::detail::aow_storage should be exposed to the public since this allows users to create container refs from preallocated storage (e.g. parquet dictionary encoding in libcudf).

This is needed to unblock #346.

Describe the solution you'd like

• Expose cuco::experimental::window type (alias of cuda::std::array<T, size>)
• Move detail::window_storage to the public namespace
• (maybe) Rename aow_storage as window_storage (or window_array?) for clarity

Describe alternatives you've considered

No response

Additional context

No response