refactor: Deprecate ddof parameter for correlation coefficient

[flowlight0]

Fix #19420

[flowlight0]

Should I change FunctionExpr::Correlation ?

[ritchie46]

Yes, we can remove ddof there I think.

[flowlight0]

Thanks for your comment! I moved ddof parameter in FunctionExpr::Correlation into CorrellationMethod::Covariance (f00ff2b) .

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.61%. Comparing base (3fad074) to head (f00ff2b).
Report is 111 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/polars-plan/src/dsl/function_expr/correlation.rs	85.71%	2 Missing ⚠️
py-polars/polars/functions/lazy.py	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20197      +/-   ##
==========================================
+ Coverage   79.47%   79.61%   +0.14%     
==========================================
  Files        1555     1564       +9     
  Lines      216318   217986    +1668     
  Branches     2456     2478      +22     
==========================================
+ Hits       171919   173559    +1640     
- Misses      43841    43858      +17     
- Partials      558      569      +11     

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[ritchie46]

Thank you @flowlight0 👍

[alexander-beedie]

初めてのPR、ありがとうございます！