feat: Add array.eval

[coastalwhite]

This implements array.eval which allows running arbitrary expressions on array elements. This is the counterpart of list.eval but for the Array datatype.

>>> import polars as pl
>>> s = pl.Series("a", [[1, 4], [8, 5], [3, 2]], pl.Array(pl.Int64, 2))
>>> s.arr.eval(pl.element().rank())
shape: (3,)
Series: 'a' [array[f64, 2]]
[
	[1.0, 2.0]
	[2.0, 1.0]
	[2.0, 1.0]
]

The arr.eval method by default only allows-for length-preserving expressions to be run and will map from an Array datatype with a certain width to another Array with the same width.

If you want to run any non-length-preserving expression, you can set as_list=True which will cause the expression to output a List.

>>> s = pl.Series(
...     "a", [["A", "B", "C"], ["C", "C", "D"], ["D", "E", "E"]], pl.Array(pl.String, 3)
... )
>>> s.arr.eval(pl.element().unique(), as_list=True)
shape: (3,)
Series: 'a' [list[str]]
[
	["C", "B", "A"]
	["C", "D"]
	["D", "E"]
]

xref: #21302.

[codecov]

Codecov Report

❌ Patch coverage is 89.09774% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.79%. Comparing base (e54330b) to head (10b7d54).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-arrow/src/array/list/mod.rs	0.00%	10 Missing ⚠️
crates/polars-core/src/chunked_array/mod.rs	93.18%	6 Missing ⚠️
crates/polars-expr/src/expressions/eval.rs	94.73%	5 Missing ⚠️
crates/polars-plan/src/dsl/expr/mod.rs	83.33%	3 Missing ⚠️
crates/polars-core/src/frame/group_by/position.rs	71.42%	2 Missing ⚠️
crates/polars-plan/src/dsl/format.rs	0.00%	2 Missing ⚠️
crates/polars-plan/src/plans/aexpr/mod.rs	94.73%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #24472    +/-   ##
========================================
  Coverage   81.78%   81.79%            
========================================
  Files        1681     1684     +3     
  Lines      228078   228785   +707     
  Branches     2923     2929     +6     
========================================
+ Hits       186533   187129   +596     
- Misses      40812    40919   +107     
- Partials      733      737     +4     

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[ritchie46]

Where do we check if len * width < IdxSize::MAX?