debug: support Hermitian weights in PredictiveController

[franckgaga]

Constructing with e.g.:

mpc = LinMPC(model, M_Hp=Hermitian(diagm(ones(10)))

was crashing. I added generic dispatch to convert correctly and handle all matrix types correctly.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.70%. Comparing base (61de78d) to head (debae4d).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/general.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #215      +/-   ##
==========================================
- Coverage   98.74%   98.70%   -0.05%     
==========================================
  Files          26       26              
  Lines        4306     4308       +2     
==========================================
  Hits         4252     4252              
- Misses         54       56       +2     

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