LinearAlgebra._generic_mat[vec/mat]mul! prefers plain alpha & beta

[dkarrasch]

The LinearAlgebra functions were refactored and accept plain alpha and beta. Potential MulAddMuls are destructured.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.31%. Comparing base (3ab784c) to head (27df57e).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #691      +/-   ##
==========================================
- Coverage   84.35%   84.31%   -0.05%     
==========================================
  Files          13       13              
  Lines        9347     9346       -1     
==========================================
- Hits         7885     7880       -5     
- Misses       1462     1466       +4     

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