[CanReader]

• pin the cuda build to ubuntu 24.04

What this changes

The CUDA build job runs on ubuntu-24.04 instead of ubuntu-latest.

Why

ubuntu-latest now resolves to 26.04. The toolkit action follows the image and asks NVIDIA's ubuntu2604 repository for cuda-13-2, which is not published there yet, so every CUDA build job fails before compiling anything (first seen on #72, which only touches src/data). The release workflow already pins its CUDA build to a fixed Ubuntu version for the same kind of reason.

How it was verified

• cargo test passes
• cargo clippy --all-targets -- -D warnings is clean
• Ran cuda_parity on a GPU
• Trained an example in --release
• No GPU here, CUDA side not runtime tested

Workflow only. This PR's own CUDA build job is the test.

Checklist

• Every new or changed backward rule has a gradcheck case
• Every new kernel has a cuda_parity case
• tensor/ops and autograd/ops still mirror each other
• Public items have /// docs