refactor: Use Scalar instead of Series some aggregations

[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

```diff @@ 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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