#2172 setup: install the CUDA Toolkit on Debian 12/13 too, not Ubuntu only

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The CUDA apt repo keyring and cuda-toolkit-13-x packages exist for debian12/debian13 as well as ubuntu2204/ubuntu2404, so derive the repo name from /etc/os-release instead of hardcoding ubuntu. Debian 13's repo carries no cuda-toolkit-13-0, so try 13-0..13-5 in order (Ubuntu still gets 13-0 first, same as before).

Checked with tools/test_setup_cuda_repo.py (4 tests, no GPU or network needed): repo mapping for ubuntu/debian/other and the minor-version fallback.

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