DataFrame.to_struct should have optional name

[deanm0000]

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(
    [
        pl.Series("a", [1, 2, 3], dtype=pl.Int64),
        pl.Series("b", [2, 3, 4], dtype=pl.Int64)
    ]
)
### Can't do
df.to_struct()
## Can only do 
df.to_struct('')

There isn't a similar restriction on the Series initiator because we can do

pl.Series(values=[{'a':1, 'b':2}, {'a':2, 'b':4}])

Log output

No response

Issue description

Should make name optional.

Expected behavior

Should have same behavior as pl.Series constructor. It's, obviously, not a big deal but it'd be nice.

Installed versions

--------Version info---------
Polars:               0.19.18
Index type:           UInt32
Platform:             Linux-5.10.102.1-microsoft-standard-WSL2-x86_64-with-glibc2.31
Python:               3.10.13 (main, Nov  1 2023, 14:20:38) [GCC 10.2.1 20210110]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          3.0.0
connectorx:           0.3.1
deltalake:            <not installed>
fsspec:               2023.10.0
gevent:               <not installed>
matplotlib:           3.8.1
numpy:                1.26.1
openpyxl:             3.1.2
pandas:               2.1.2
pyarrow:              14.0.0
pydantic:             <not installed>
pyiceberg:            <not installed>
pyxlsb:               1.0.10
sqlalchemy:           2.0.23
xlsx2csv:             0.8.1
xlsxwriter:           3.1.9

[alexander-beedie]

The default Series name if not specified is indeed the empty string - doesn't seem unreasonable to be consistent here ;)