pl.len() gives wrong results when evaluated on LazyFrame that contains a broadcasted scalar

[colin-kerkhof]

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

base = pl.DataFrame({"a": [1, 2, 3]})

lazy_len = base.lazy().select(
    pl.col("a"),
    pl.lit(list, allow_object=True).first(),
).select(pl.len()).collect()

df_len = base.select(
    pl.col("a"),
    pl.lit(list, allow_object=True).first(), 
).select(pl.len())

lazy_len.equals(df_len) # False

Log output

No response

Issue description

When using pl.len() on a LazyFrame, after using a scalar series that needs to be broadcasted, it returns 1 as a value instead of the actual number of rows. Collecting without selecting pl.len yields the correct output

Expected behavior

The actual number of rows from the dataframe

Installed versions

Polars:              1.15.0
Index type:          UInt32
Platform:            macOS-15.1.1-arm64-arm-64bit
Python:              3.12.7 (main, Oct  1 2024, 02:05:46) [Clang 16.0.0 (clang-1600.0.26.3)]
LTS CPU:             False

----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
boto3                1.35.60
cloudpickle          <not installed>
connectorx           <not installed>
deltalake            0.22.0
fastexcel            <not installed>
fsspec               2024.10.0
gevent               <not installed>
google.auth          <not installed>
great_tables         <not installed>
matplotlib           3.9.2
nest_asyncio         1.6.0
numpy                2.1.3
openpyxl             <not installed>
pandas               2.2.3
pyarrow              18.0.0
pydantic             2.9.2
pyiceberg            <not installed>
sqlalchemy           2.0.36
torch                2.5.1
xlsx2csv             <not installed>
xlsxwriter           <not installed>