Add a hicsparse backend to linalg sparse

[l90lpa]

This PR adds a hicsparse backend to the sparse matrix multiplication routines of linalg sparse.

This PR depends on #247 and the branch of this PR is currently based on the branch of #247.

Notes:

• This PR previously depended on Add GPU offload capable sparse matrix #241 but that dependency is nolonger necessary as Add GPU offloadable SparseMatrixStorage and read-only SparseMatrixView. #247 will superseded the former PR.

[l90lpa]

I've rebased this PR as its dependency has now changed from #241 to #247 (see comment #247 (comment)).

[wdeconinck]

This looks nearly perfect. Very nice work, thanks! 🙏
I rebased it on develop which now contains the dependent #247 .
What's missing still is support for having the SourceValue and TargetValue be of a different precision than the MatrixValue.
This is e.g. the case with the OpenMP backend. The matrix is typically double precision (eckit::linalg::Scalar), whereas the SourceValue and TargetValue come from the atlas Fields which can be single or double.
Check e.g. this hicsparse_matrix_multiply in https://github.com/ecmwf/atlas/blob/develop/src/tests/linalg/test_linalg_sparse_matrix_gpu.cc#L32 showing the different precisions.
Note that alpha and beta arguments need to be of a chosen "ComputeType". In above linked routine I chose ComputeType to match the MatrixValue type, but in principle that is another user-choice that could be made...

[wdeconinck]

Possibly this hicsparse backend only works for fields which are contiguous in memory, e.g. not separate slices of a larger array with stride != 1.
We may need to abort if that is the case. It would be good to test.