Skip feature importance

[egillax]

Added a flag skip_importance to skip calculating the feature importance. Solves #89 . Also added tests to confirm the flag works. Ran tests locally and they passed.

[codecov]

Codecov Report

Merging #91 (21aaad2) into main (c2e5f25) will increase coverage by 87.53%.
The diff coverage is 87.09%.

❗ Current head 21aaad2 differs from pull request most recent head e46a52e. Consider uploading reports for the commit e46a52e to get more accurate results

@@            Coverage Diff             @@
##            main      #91       +/-   ##
==========================================
+ Coverage   0.00%   87.53%   +87.53%     
==========================================
  Files         10       10               
  Lines       1054     1051        -3     
==========================================
+ Hits           0      920      +920     
+ Misses      1054      131      -923     

Impacted Files	Coverage Δ
R/model.R	94.59% <84.00%> (+94.59%)	⬆️
R/pretraining.R	94.30% <100.00%> (+94.30%)	⬆️
R/sparsemax.R	65.51% <0.00%> (+65.51%)	⬆️
R/hardhat.R	88.94% <0.00%> (+88.94%)	⬆️
R/explain.R	92.30% <0.00%> (+92.30%)	⬆️
R/parsnip.R	99.08% <0.00%> (+99.08%)	⬆️
R/plot.R	100.00% <0.00%> (+100.00%)	⬆️
R/tab-network.R	100.00% <0.00%> (+100.00%)	⬆️

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[cregouby]

Thanks a lot @egillax ! Would you be kind to add a line in the NEWS.md file ? (and maybe add your name in the author list in the DESCRIPTION.md if you wish)

[cregouby]

Great job ! Thanks @egillax