[Skill]: Refactor style and test skills to point to developer documentation where possible

The cccl-style and cccl-test skills introduced in https://github.com/NVIDIA/cccl/pull/9405 (refactored from the libcudacxx-style and libcudacxx-test introduced previously) are meant for agents working in CCCL (both writing and reviewing code) to understand code style. It was pointed out that there is some overlap with developer documentation.

#2635 attempts to add a unified source of developer guidelines and code style to our documentation. Once we close that issue, we should look into how the style and test skills (and potentially other internal skills) should interact with the developer documentation. The most straightforward solution is to simply have the skills point to the documentation files, but we need to study the effectiveness of that approach vs having the guidelines being spelled out in the skill file directly