BUGFIX: Update preconditioner in cg

[IvanBioli]

After the formatting of the repository in #1150 , a small error was introduced in the update_state! function in the src/multivariate/solvers/first_order/cg.jl file: the preconditioner is not updated at every iteration, but only at the first one. The change ensures that the _apply_precondprep method is called. Changes:

• src/multivariate/solvers/first_order/cg.jl: Added a call to _apply_precondprep(method, state.x)

[github-actions]

Benchmark Results

	master	3f65f67...	master / 3f65f67...
multivariate/solvers/first_order/AdaMax	0.643 ± 0.0082 ms	0.645 ± 0.008 ms	0.997 ± 0.018
multivariate/solvers/first_order/Adam	0.644 ± 0.008 ms	0.645 ± 0.0079 ms	0.998 ± 0.017
multivariate/solvers/first_order/BFGS	0.224 ± 0.0038 ms	0.224 ± 0.0043 ms	1 ± 0.026
multivariate/solvers/first_order/ConjugateGradient	0.0485 ± 0.00065 ms	0.0483 ± 0.00064 ms	1 ± 0.019
multivariate/solvers/first_order/GradientDescent	1.71 ± 0.014 ms	1.71 ± 0.012 ms	1 ± 0.011
multivariate/solvers/first_order/LBFGS	0.22 ± 0.0038 ms	0.219 ± 0.0083 ms	1 ± 0.042
multivariate/solvers/first_order/MomentumGradientDescent	2.51 ± 0.018 ms	2.5 ± 0.012 ms	1 ± 0.0086
multivariate/solvers/first_order/NGMRES	0.555 ± 0.011 ms	0.555 ± 0.011 ms	1 ± 0.028
time_to_load	0.525 ± 0.0036 s	0.529 ± 0.0022 s	0.993 ± 0.008

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).

[pkofod]

Thanks for noticing, can you link to the line in question? I don't see any changes to cg.jl in that pr :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.71%. Comparing base (6850998) to head (3f65f67).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1177   +/-   ##
=======================================
  Coverage   85.70%   85.71%           
=======================================
  Files          46       46           
  Lines        3596     3597    +1     
=======================================
+ Hits         3082     3083    +1     
  Misses        514      514           

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[IvanBioli]

Thanks for noticing, can you link to the line in question? I don't see any changes to cg.jl in that pr :)

I added _apply_precondprep(method, state.x) at line 187