feat(python): Implement Struct support for Series.to_numpy

[stinodego]

Ref #14334

We choose to represent Structs as a 2D array. It's constructed by unnesting and calling DataFrame.to_numpy.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 81.38%. Comparing base (825eb9c) to head (5cf918c).
Report is 1 commits behind head on main.

Files	Patch %	Lines
py-polars/src/interop/numpy/to_numpy_series.rs	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16383      +/-   ##
==========================================
+ Coverage   81.36%   81.38%   +0.01%     
==========================================
  Files        1406     1406              
  Lines      183911   183911              
  Branches     2954     2954              
==========================================
+ Hits       149648   149676      +28     
+ Misses      33750    33722      -28     
  Partials      513      513              

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