Enhance column selection to support Polars expressions

[jrycw]

Related to #340.

This PR aims to extend column selection to support Polars expressions.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.51%. Comparing base (7eae1f2) to head (25774f2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #346   +/-   ##
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  Coverage   83.51%   83.51%           
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  Files          41       41           
  Lines        4308     4308           
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  Hits         3598     3598           
  Misses        710      710           

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[machow]

Thanks for taking the time to implement this---I left some thoughts in the comments. I'm open to this, but trying to get a feel for where the selection API is going? (suspecting it might not change too much?). If it's okay with you, let's wait a bit and collect more info on the pl.col() vs selector situation.

[jrycw]

@machow , thank you for your response. Let's hold off for now and see how things progress. I'll mark this PR as a draft for the time being. On another note, it appears that our project is gaining more attention from the community. I suggest that we tidy up the finished issues before the next minor release (0.6.0). This way, future contributors can easily identify and tackle the issues they want to help with.

[jrycw]

I'll close this PR since the column selection of Polars is being refactored through #360 and is included in version 0.6.1.