added specialized method for 3-argument dot with diagonal matrix

[matbesancon]

Closes #563

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 3 lines in your changes missing coverage. Please review.

Project coverage is 84.13%. Comparing base (313a04f) to head (031c5fd).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/linalg.jl	92.30%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #565      +/-   ##
==========================================
+ Coverage   84.09%   84.13%   +0.04%     
==========================================
  Files          12       12              
  Lines        9102     9159      +57     
==========================================
+ Hits         7654     7706      +52     
- Misses       1448     1453       +5     

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[dkarrasch]

Nice. The comments refer to both methods actually. As for the length checks, perhaps you could add tests for all mismatching cases?