Add CUDA 13.2 support (#20267)
## Summary
Add CUDA 13.2 to the supported PyTorch backends. `--torch-backend=cu132`
and `UV_TORCH_BACKEND=cu132` now use the CUDA 13.2 index, and `auto`
prefers it on compatible Linux and Windows drivers.
Closes https://github.com/astral-sh/uv/issues/20235.
