Reformat the gaussian conditional sampler

[lionelkusch]

I reformat the Gaussian estimation of knockoff in the format of classes, as conditional sampling.
I moved all the conditional samplers into statistical_tool.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (319b433) to head (43be183).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #366      +/-   ##
==========================================
- Coverage   99.43%   99.38%   -0.06%     
==========================================
  Files          22       20       -2     
  Lines        1247     1140     -107     
==========================================
- Hits         1240     1133     -107     
  Misses          7        7              

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[bthirion]

Thx for this refactoring. I have two relatively minor comments.

[jpaillard]

Thanks, I agree that having both samplers implemented as classes makes sense.

[jpaillard]

I think it limits extra work to integrate the test in this PR rather than having to fix something in an upcoming one. I made a suggestion for the tests.

[bthirion]

The PR is almost ready to merge

[bthirion]

Needs a bit of fine tuning.

[bthirion]

Given #488, I have no further comments than @jpaillard's ones.

[jpaillard]

Thank you for the changes