Update the deprecated MKL sparse API

[wdeconinck]

From IntelMKL 2026.0 the used deprecated MKL sparse functions are no longer available. I noticed eckit with MKL does not compile when upgrading to use the most recent intel-oneapi-toolkit, including MKL.

This pull request modernizes and simplifies the MKL-based sparse linear algebra implementation by replacing deprecated MKL routines with their recommended alternatives and introducing robust resource management. The changes improve code safety, maintainability, and compatibility with IntelMKL 2026.0.

Refactoring and modernization:

• Replaced deprecated MKL routines (mkl_dcsrmv and mkl_dcsrmm) with the modern mkl_sparse_d_mv and mkl_sparse_d_mm APIs in the spmv and spmm methods of LinearAlgebraMKL, improving compatibility and maintainability. [1] [2]

Resource management and error handling:

• Introduced a MKLSparseHandle RAII helper struct to manage sparse_matrix_t lifetimes and ensure proper cleanup, reducing the risk of memory/resource leaks.
• Added utility functions (checkSparseStatus, generalMatrixDescription, createSparseMatrixHandle) for safer error handling and clearer construction of MKL sparse matrix descriptors and handles.### Description

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌦️ >> Documentation << 🌦️
https://sites.ecmwf.int/docs/dev-section/eckit/pull-requests/PR-295

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.46%. Comparing base (c90f85c) to head (03a823e).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #295   +/-   ##
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  Coverage    66.46%   66.46%           
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  Files         1128     1128           
  Lines        57844    57844           
  Branches      4408     4408           
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+ Hits         38446    38447    +1     
+ Misses       19398    19397    -1     

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[pmaciel]

I'm very happy with this, it comes at a great time too! Merge away 👍

[wdeconinck]

Thank you @pmaciel for the lighting quick review. Just waiting for @simondsmart still.