WIP add weights to Group Lasso

[Badr-MOUFAD]

closes #219

[codecov-commenter]

Codecov Report

Merging #220 (de64d55) into main (f7fa260) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #220      +/-   ##
==========================================
+ Coverage   85.79%   85.80%   +0.01%     
==========================================
  Files          14       14              
  Lines         929      930       +1     
  Branches      128      128              
==========================================
+ Hits          797      798       +1     
  Misses        101      101              
  Partials       31       31              

Flag	Coverage Δ
unittests	∅ <ø> (∅)

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Impacted Files	Coverage Δ
celer/dropin_sklearn.py	95.71% <100.00%> (+0.03%)	⬆️

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[mathurinm]

@Badr-MOUFAD you need to add a unit test to check that it works as expected, for example by comparing with a Lasso in the case where groups are of size 1. You can draw inspiration from the existing test on weights for the Lasso