PanicException: arg_sort operation not supported for dtype struct

[cmdlineluser]

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Issue description

This was fixed for DataFrame.sort in #7777

I just encountered it again trying to use .rank() + .over()

.sort() + .over() also raises the same exception.

.sort() succeeds without .over().

.rank() still raises the exception without .over()

Reproducible example

import polars as pl

df = pl.DataFrame({
   'row_id':[1,2,3,4,5,6,7,8,9,10],
   'Group':[1,1,1,1,1,2,2,2,2,2],
   'Var1':[100,100,100,200,200,300,300,400,400,400],
   'Var2':[5,5,6,7,8,1,1,2,2,3]
})

# PanicException: `arg_sort` operation not supported for dtype `struct[2]`
df.with_columns(pl.struct("Var1", "Var2").rank().over("Group"))

# PanicException: `arg_sort` operation not supported for dtype `struct[2]`
df.with_columns(pl.struct("Var1", "Var2").sort().over("Group"))

# PanicException: `arg_sort` operation not supported for dtype `struct[2]`
df.with_columns(pl.struct("Var1", "Var2").rank())

# OK
df.with_columns(pl.struct("Var1", "Var2").sort())

Expected behavior

No exception.

Installed versions

---Version info---
Polars: 0.16.18
Index type: UInt32
Python: 3.10.9 (main, Jan 14 2023, 16:56:26)
---Optional dependencies---
numpy: 1.23.5
pandas: 2.0.0
pyarrow: 9.0.0
connectorx: <not installed>
deltalake: <not installed>
fsspec: 2022.8.2
matplotlib: 3.5.1
xlsx2csv: 0.8
xlsxwriter: 3.0.8