feat(rust): Add split_at method to arrow Array

[coastalwhite]

This adds a split_at and split_at_unchecked method to each type that implements the Array trait. This is done under the Splitable trait.

[codecov]

Codecov Report

Attention: Patch coverage is 83.52601% with 57 lines in your changes are missing coverage. Please review.

Project coverage is 81.50%. Comparing base (d190e02) to head (cf3a8c0).
Report is 10 commits behind head on main.

❗ Current head cf3a8c0 differs from pull request most recent head b473cb9

Please upload reports for the commit b473cb9 to get more accurate results.

Files	Patch %	Lines
crates/polars-core/src/chunked_array/object/mod.rs	0.00%	27 Missing ⚠️
crates/polars-arrow/src/array/null.rs	0.00%	15 Missing ⚠️
crates/polars-arrow/src/array/binview/mod.rs	76.31%	9 Missing ⚠️
crates/polars-arrow/src/array/mod.rs	87.09%	4 Missing ⚠️
crates/polars-arrow/src/bitmap/immutable.rs	92.59%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16620      +/-   ##
==========================================
- Coverage   81.51%   81.50%   -0.01%     
==========================================
  Files        1414     1414              
  Lines      185714   186252     +538     
  Branches     3008     3027      +19     
==========================================
+ Hits       151385   151810     +425     
- Misses      33813    33911      +98     
- Partials      516      531      +15     

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