nulls_last parameter not honored while sorting an already sorted array

[siddharth-vi]

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

df = pl.DataFrame({
    "a": [1,2,None,3],
})
# nulls first
print(df.sort("a"))
# shape: (4, 1)
# ┌──────┐
# │ a    │
# │ ---  │
# │ i64  │
# ╞══════╡
# │ null │
# │ 1    │
# │ 2    │
# │ 3    │
# └──────┘
# nulls last as expected
print(df.sort("a",nulls_last=True))
# shape: (4, 1)
# ┌──────┐
# │ a    │
# │ ---  │
# │ i64  │
# ╞══════╡
# │ 1    │
# │ 2    │
# │ 3    │
# │ null │
# └──────┘
# nulls should be last
print(df.sort("a").sort("a",nulls_last=True))
# shape: (4, 1)
# ┌──────┐
# │ a    │
# │ ---  │
# │ i64  │
# ╞══════╡
# │ null │
# │ 1    │
# │ 2    │
# │ 3    │
# └──────┘

Log output

No response

Issue description

This is due to a missing check in fast path

Expected behavior

nulls_last should be honored

Installed versions

--------Version info---------
Polars:              1.14.0
Index type:          UInt32
Platform:            Linux-5.15.0-112-generic-x86_64-with-glibc2.35
Python:              3.12.7 | packaged by Anaconda, Inc. | (main, Oct  4 2024, 13:27:36) [GCC 11.2.0]
LTS CPU:             False

----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
boto3                <not installed>
cloudpickle          <not installed>
connectorx           <not installed>
deltalake            <not installed>
fastexcel            <not installed>
fsspec               <not installed>
gevent               <not installed>
google.auth          <not installed>
great_tables         <not installed>
matplotlib           <not installed>
nest_asyncio         1.6.0
numpy                2.1.2
openpyxl             <not installed>
pandas               2.2.3
pyarrow              <not installed>
pydantic             <not installed>
pyiceberg            <not installed>
sqlalchemy           <not installed>
torch                <not installed>
xlsx2csv             <not installed>
xlsxwriter           <not installed>