added diagonal-sparse multiplication

[matbesancon]

Adds a specialization for the out-of-place multiplication of Diagonal * sparse-vector, otherwise the current version was O(n) instead of O(nnz)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.16%. Comparing base (313a04f) to head (eedb426).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #564      +/-   ##
==========================================
+ Coverage   84.09%   84.16%   +0.07%     
==========================================
  Files          12       12              
  Lines        9102     9172      +70     
==========================================
+ Hits         7654     7720      +66     
- Misses       1448     1452       +4     

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[matbesancon]

@dkarrasch this should be good to go too