perf: Use split_at instead of double slice in chunk splits.

[ritchie46]

Can add this to more splitting functionality.

[codecov]

Codecov Report

Attention: Patch coverage is 37.12871% with 127 lines in your changes missing coverage. Please review.

Project coverage is 81.33%. Comparing base (3fe4cfe) to head (707664a).

Files	Patch %	Lines
...ates/polars-core/src/chunked_array/ops/chunkops.rs	58.02%	34 Missing ⚠️
...tes/polars-core/src/series/implementations/null.rs	0.00%	17 Missing ⚠️
.../polars-core/src/series/implementations/decimal.rs	0.00%	10 Missing ⚠️
...polars-core/src/series/implementations/datetime.rs	0.00%	9 Missing ⚠️
.../polars-core/src/series/implementations/struct_.rs	0.00%	7 Missing ⚠️
...ars-core/src/series/implementations/categorical.rs	0.00%	6 Missing ⚠️
...polars-core/src/series/implementations/duration.rs	0.00%	6 Missing ⚠️
crates/polars-core/src/utils/mod.rs	50.00%	6 Missing ⚠️
...es/polars-core/src/series/implementations/array.rs	0.00%	4 Missing ⚠️
...s/polars-core/src/series/implementations/binary.rs	0.00%	4 Missing ⚠️
... and 6 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16856      +/-   ##
==========================================
- Coverage   81.37%   81.33%   -0.05%     
==========================================
  Files        1425     1425              
  Lines      187669   187867     +198     
  Branches     2702     2702              
==========================================
+ Hits       152720   152794      +74     
- Misses      34453    34577     +124     
  Partials      496      496              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.