P3371R5: Fix C++26 by making the rank-1, rank-2, rank-k, and rank-2k updates consistent with the BLAS

**Link:** https://wg21.link/P3371R5

Feature-test macros (increased):
```c++
#define __cpp_lib_linalg 202511L // also in
```

Start with P3371R5 and the existing implementation. Compare the rank-1, rank-2, rank-k, and rank-2k update requirements with the BLAS behavior, including the requested __cpp_lib_linalg value of 202511L. Done means the operations are consistent with the paper and the feature-test macro is updated.

Written by the indexing model from the issue text.