Update SpMVOp to new cuSPARSE API and revise default CUDA architectures

[ZedongPeng]

Summary

• SpMVOp: adapt to the new cusparseSpMVOp API in cuSPARSE 12.8.1 (CUDA 13.3), which added a cusparseSpMVOpAlg_t parameter — pass CUSPARSE_SPMVOP_ALG2 explicitly and bump the version gate from 12703 to 12801. Older toolkits keep the classic cusparseSpMV path.
• CMake: replace the fixed 60 70 75 80 86 89 90 default with per-toolkit architecture lists (adds Blackwell on CUDA ≥ 12.8, drops pre-Turing on CUDA 13), each with SASS for all supported archs + PTX only for the newest. CMAKE_CUDA_ARCHITECTURES / CUDAARCHS overrides still respected.
• Docs: update README for the new SpMV backend version gate.