fix!: Remove supertype definition of List and non-List types

[stinodego]

Closes #10920

Various operations would add nesting levels on behalf of the user. We will now raise an error instead. The user should manually cast their data to a List if they want to combine their non-List data with List data.

Example

Before:

>>> s1 = pl.Series(["a", "b"])
>>> s2 = pl.Series([["x", "y"], ["z"]])
>>> pl.concat([s1, s2])
shape: (4,)
Series: '' [list[str]]
[
        ["a"]
        ["b"]
        ["x", "y"]
        ["z"]
]

After:

>>> pl.concat([s1, s2])
Traceback (most recent call last):
...
polars.exceptions.SchemaError: type List(String) is incompatible with expected type String

Use instead:

>>> s1_list = s1.cast(pl.List(s1.dtype))
>>> pl.concat([s1_list, s2])
shape: (4,)
Series: '' [list[str]]
[
        ["a"]
        ["b"]
        ["x", "y"]
        ["z"]
]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.09%. Comparing base (f7cca90) to head (8439a9e).
Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16918      +/-   ##
==========================================
- Coverage   81.43%   81.09%   -0.35%     
==========================================
  Files        1425     1435      +10     
  Lines      187973   189553    +1580     
  Branches     2704     2712       +8     
==========================================
+ Hits       153074   153710     +636     
- Misses      34402    35343     +941     
- Partials      497      500       +3     

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

[codspeed-hq]

CodSpeed Performance Report

Merging #16918 will degrade performances by 15.93%

_{Comparing list-supertype (8439a9e) with main (9914d96)}

Summary

❌ 1 regressions
✅ 36 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	list-supertype	Change
❌	test_groupby_h2oai_q1	2.3 ms	2.8 ms	-15.93%