pl.struct usage of schema renders keyword argument renaming ineffective

[SandroCasagrande]

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


pl.DataFrame({"a": 1}).select(
    s = pl.struct(schema={"b": pl.Int64}, b = pl.col("a")),
)

Log output

polars.exceptions.ColumnNotFoundError: b

Issue description

I'm using the named_exprs parameter of pl.struct to easily name fields as explained in the docstring and expect it to act identically to expressions in exprs with an additional alias. This is exactly what happens initially in source, but then the derived alias remains unused since expressions become rebuilt after https://github.com/pola-rs/polars/blame/d856b4987091dce730d8d0c4ffc08b14bf48f8cc/py-polars/polars/functions/as_datatype.py#L585-L586. I guess the check should include not named_exprs, too?

Expected behavior

Identical to

pl.DataFrame({"a": 1}).select(
    s = pl.struct(pl.col("a").alias("b"), schema={"b": pl.Int64})
)

Installed versions

--------Version info---------
Polars:               0.20.30
Index type:           UInt32
Platform:             macOS-14.5-arm64-arm-64bit
Python:               3.11.9 (main, Apr 19 2024, 11:43:47) [Clang 14.0.6 ]
----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          <not installed>
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            <not installed>
fsspec:               2024.3.1
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           <not installed>
nest_asyncio:         <not installed>
numpy:                1.26.4
openpyxl:             3.1.2
pandas:               2.2.2
pyarrow:              16.0.0
pydantic:             2.7.1
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           2.0.30
torch:                <not installed>
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>