refactor: Use Scalar instead of Series some aggregations

[ritchie46]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 84.67967% with 55 lines in your changes are missing coverage. Please review.

Project coverage is 80.80%. Comparing base (98a2d9b) to head (bb4631a). Report is 3 commits behind head on main.

Files	Patch %	Lines
...polars-core/src/chunked_array/ops/aggregate/mod.rs	78.31%	18 Missing :warning:
...polars-core/src/series/implementations/duration.rs	84.90%	8 Missing :warning:
crates/polars-core/src/series/series_trait.rs	0.00%	8 Missing :warning:
...s/polars-core/src/series/implementations/binary.rs	0.00%	4 Missing :warning:
py-polars/src/series/aggregation.rs	80.95%	4 Missing :warning:
crates/polars-core/src/datatypes/any_value.rs	81.25%	3 Missing :warning:
...polars-core/src/series/implementations/datetime.rs	78.57%	3 Missing :warning:
...rates/polars-ops/src/chunked_array/list/min_max.rs	70.00%	3 Missing :warning:
.../polars-core/src/series/implementations/decimal.rs	88.88%	2 Missing :warning:
crates/polars-core/src/series/mod.rs	96.29%	1 Missing :warning:
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16277      +/-   ##
==========================================
- Coverage   80.82%   80.80%   -0.02%     
==========================================
  Files        1393     1393              
  Lines      179341   179426      +85     
  Branches     2918     2921       +3     
==========================================
+ Hits       144955   144990      +35     
- Misses      33884    33933      +49     
- Partials      502      503       +1     

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