DataFrame.group_by.head fails with Decimal types.

[sernst]

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, 3], 
        "b": ["1.123", "2.234", "3.345"]
    })
    # Comment out the decimal conversion and the code works. Only errors when b is Decimal dtype.
    .with_columns(pl.col("b").str.to_decimal())
    .group_by("a")
    .head(1)
)

Log output

thread 'polars-0' panicked at crates/polars-core/src/series/series_trait.rs:82:13:
`explode_by_offsets` operation not supported for dtype `decimal[*,3]`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "../site-packages/polars/dataframe/group_by.py", line 376, in head
    .collect(no_optimization=True)
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "../site-packages/polars/lazyframe/frame.py", line 1943, in collect
    return wrap_df(ldf.collect())
                   ^^^^^^^^^^^^^
pyo3_runtime.PanicException: `explode_by_offsets` operation not supported for dtype `decimal[*,3]`

Issue description

I've tested this on both Linux (Ubuntu 22.04) and Windows and it fails with the same behavior.

Expected behavior

I would expect the head to work in the same fashion as in the case where the "b" column is a string type instead of a decimal type.

Installed versions

--------Version info---------
Polars:               0.20.16
Index type:           UInt32
Platform:             Linux-5.15.133.1-microsoft-standard-WSL2-x86_64-with-glibc2.35
Python:               3.12.2 (main, Feb 25 2024, 16:35:05) [GCC 11.4.0]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          <not installed>
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            <not installed>
fsspec:               <not installed>
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           <not installed>
numpy:                <not installed>
openpyxl:             <not installed>
pandas:               <not installed>
pyarrow:              <not installed>
pydantic:             <not installed>
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           <not installed>
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>

--------Version info---------
Polars:               0.20.16
Index type:           UInt32
Platform:             Windows-11-10.0.22000-SP0
Python:               3.12.1 (tags/v3.12.1:2305ca5, Dec  7 2023, 22:03:25) [MSC v.1937 64 bit (AMD64)]

----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:           3.8.3
numpy:                1.26.4
openpyxl:             3.1.2
pandas:               2.2.1
pyarrow:              15.0.2
pydantic:             <not installed>
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           <not installed>
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>

[stinodego]

Looks like this hasn't been implemented yet. An implementation is welcome.