Port existing docs to Sphinx #315
Description
CUB docs were updated to use the new rst/sphinx docs system. We should update Thrust/libcudacxx docs to do the same.
### Tasks
- [ ] https://github.com/NVIDIA/cccl/issues/1742
- [x] Port libcudacxx docs to use Sphinx
- [ ] https://github.com/NVIDIA/cccl/issues/317