Null cases not handled properly for some list operations

[heshamdar]

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

test = pl.DataFrame({"a": [["hi"], [], None]})
print(test.select(pl.col("a").list.contains("hi")))

test = pl.DataFrame({"a": [["hi"], [], None]})
print(test.select(pl.col("a").list.len()))

Log output

shape: (3, 1)
┌───────┐
│ a     │
│ ---   │
│ bool  │
╞═══════╡
│ true  │
│ false │
│ false │
└───────┘
shape: (3, 1)
┌─────┐
│ a   │
│ --- │
│ u32 │
╞═════╡
│ 1   │
│ 0   │
│ 0   │
└─────┘

Issue description

Some list operations that return a non list type (e.g. contains and len) result in (arguably) incorrect values for null values. In the example above, contains returns False and len returns 0

Expected behavior

operations on null values should just return null

Installed versions

--------Version info---------
Polars:               0.20.26
Index type:           UInt32
Platform:             macOS-14.2.1-arm64-arm-64bit
Python:               3.10.4 (main, May 28 2022, 12:23:44) [Clang 13.1.6 (clang-1316.0.21.2.5)]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          3.0.0
connectorx:           <not installed>
deltalake:            0.15.3
fastexcel:            0.9.1
fsspec:               2024.3.1
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           3.8.3
nest_asyncio:         1.6.0
numpy:                1.26.4
openpyxl:             3.1.2
pandas:               2.0.3
pyarrow:              15.0.0
pydantic:             2.7.0
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           2.0.29
torch:                <not installed>
xlsx2csv:             0.8.2
xlsxwriter:           <not installed>