Refactor preconditioning code

[pkofod]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 98.24561% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.85%. Comparing base (992bb39) to head (274b697).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/multivariate/precon.jl	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1138      +/-   ##
==========================================
+ Coverage   85.81%   85.85%   +0.04%     
==========================================
  Files          46       46              
  Lines        3532     3536       +4     
==========================================
+ Hits         3031     3036       +5     
+ Misses        501      500       -1     

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[github-actions]

Benchmark Results

	master	274b697...	master / 274b697...
multivariate/solvers/first_order/AdaMax	0.65 ± 0.0077 ms	0.644 ± 0.0079 ms	1.01
multivariate/solvers/first_order/Adam	0.65 ± 0.008 ms	0.643 ± 0.008 ms	1.01
multivariate/solvers/first_order/BFGS	0.224 ± 0.0076 ms	0.222 ± 0.0043 ms	1.01
multivariate/solvers/first_order/ConjugateGradient	0.048 ± 0.0006 ms	0.0477 ± 0.00061 ms	1.01
multivariate/solvers/first_order/GradientDescent	1.71 ± 0.016 ms	1.7 ± 0.018 ms	1.01
multivariate/solvers/first_order/LBFGS	0.22 ± 0.0049 ms	0.219 ± 0.0037 ms	1.01
multivariate/solvers/first_order/MomentumGradientDescent	2.52 ± 0.02 ms	2.5 ± 0.016 ms	1.01
multivariate/solvers/first_order/NGMRES	0.554 ± 0.011 ms	0.549 ± 0.01 ms	1.01
time_to_load	0.535 ± 0.001 s	0.539 ± 0.0028 s	0.993

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).