feat: Add dy.Array column type

[jjurm]

Motivation

Dataframely currently doesn't support the pl.Array column type, and so dataframes using array columns cannot be validated. I'd like to be able to validate those, too.

Changes

This PR implements the dy.Array column type corresponding to polars' pl.Array type.

The implementation is very similar to the dy.List, however, polars List differs from Array mostly in the following ways:

• Lists are flat, whereas Arrays can have have shapes with multiple axes
• Arrays must have fixed size (or shape) whereas List elements can vary in length
• pl.Expr.arr has less functionality compared to pl.Expr.list, most notably there is no .arr.eval() function, which complicates validating rules. One option is to recursively convert the array column to nested lists just for validation, but since the performance would be suboptimal, I left this part unimplemented and only allowed Array's inner column types without any validation rules.

Would be happy to hear any feedback!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (b49692a) to head (217613b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #27   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           37        38    +1     
  Lines         1808      1845   +37     
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+ Hits          1808      1845   +37     

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[borchero]

Thank you, this looks great already! I left a couple of small comments but I think it is almost ready :)

Great job finding all the right places to add code, esp. in the tests, and thanks for maintaining the 100% coverage 😁🚀

[delsner]

Could you please also update the mypy plugin and tests/test_typing.py similar to #29? Thanks!

[borchero]

Looks good to me (modulo the mypy plugin that @delsner mentioned), thanks! 🚀

[jjurm]

Thanks a lot for the great feedback @borchero !

I am struggling to get the problem with the mypy plugin, @delsner could you please add a test for the mypy plugin that you would like to pass?

[delsner]

Great work, thanks! 🚀 I added a typing test and updated the mypy plugin code.