Add cuSPARSE safe wrapper

[g-ampo]

Add cuSPARSE safe wrapper

cuSPARSE had no safe.rs and only 2 functions in result.rs.

• result.rs: expanded to 26 functions (handle, CSR/CSC/COO/dense descriptors, SpMV, SpMM, sparse-dense conversions). Cfg-gated for CUDA 11 vs 12.
• safe.rs: RAII descriptor wrappers, spmv(), spmm() with automatic workspace management.

Tested SpMV and SpMM on RTX 3060 Ti (CUDA 13.0).

[gemini-code-assist]

Code Review

This pull request introduces safe abstractions for cuSPARSE, including high-level wrappers for handles and descriptors with automatic workspace management for SpMV and SpMM operations, alongside low-level FFI wrappers supporting CUDA 11 and 12. Feedback identifies critical safety issues where descriptors must hold a reference to the CUDA context to prevent undefined behavior during destruction. Additionally, several destruction functions in the low-level API contain incorrect type casts for CUDA 12, and safe wrappers for format conversions are currently missing from the implementation.

[chelsea0x3b]

Hey I'm gonna be honest, this PR is way too big for me to review and needs to be split into multiple sub PRs. I appreciate the use of agents, but this is not set up nicely for me.

Did you run the tests?