Casting Array to another Array ignores width changes

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Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl

s = pl.Series([[1, 2], [3, 4]], dtype=pl.Array(pl.Int8, 2))
result = s.cast(pl.Array(pl.Int8, 4))
print(s)

Log output

shape: (2,)
Series: '' [array[i8, 2]]
[
        [1, 2]
        [3, 4]
]

Issue description

Casting an array to an array of a different width leads to a faulty state.

Expected behavior

This operation should either be prohibited or it should reshape the array and result in:

shape: (1,)
Series: '' [array[i8, 4]]
[
        [1, 2, 3, 4]
]

Installed versions

main

[stinodego]

Discussed with Ritchie, and the intended behavior is raising an error (not reshaping).