feat(datatypes): support fixed length arrays

[dgarridoa]

What happened?

Hi, the Table.to_polars method cast list type to array type, I would like to preserve the original data type.

Reproducible example:

import ibis
import numpy as np
import polars as pl


ibis.set_backend("polars")

df = pl.DataFrame({x: np.random.random((100, 10)) })
>>> df.schema
Schema([('x', Array(Float64, shape=(10,)))])

t = ibis.memtable(df)
>>> t.schema()
ibis.Schema {
  x  array<float64>
}

>>> t.to_polars().schema
Schema([('x', List(Float64))])

What version of ibis are you using?

ibis-framework==10.0.0

What backend(s) are you using, if any?

polars==1.22.0

Relevant log output

Code of Conduct

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[cpcloud]

This is working as intended right now, as we don't support fixed length arrays at the moment.