Replace `__attribute__((unused))` with `[[maybe_unused]]` to fix [msvc error](https://github.com/google/jax/actions/runs/8630859524/job/23658055502).
Replace `__attribute__((unused))` with `[[maybe_unused]]` to fix [msvc error](https://github.com/google/jax/actions/runs/8630859524/job/23658055502).
