[FEA] Support `pl.corr` in cudf-polars

```python
import polars as pl
pl.Config.set_verbose(True)

lf = pl.LazyFrame(
{
"a": [1, 2, 3, 4, 5, 6],
"b": [1, 2, 3, 4, 5, 6],
"g": ["x", "x", "x", "y", "y", "y"],
}
)

print(lf.select(pl.corr('a', 'b')).collect(engine='gpu'))
print(lf.group_by('g').agg(pl.corr('a', 'b')).collect(engine='gpu'))

"""
/opt/miniconda3_py312/lib/python3.12/site-packages/polars/lazyframe/frame.py:2407: PerformanceWarning: Query execution with GPU not possible: unsupported operations.
The errors were:
- NotImplementedError: corr
return wrap_df(ldf.collect(engine, callback))
"""
````

The cudf-polars version is '25.12.00a362'