.list.product

### Description

If there's `.list.sum`, perhaps `.list.product` would also be in-scope?

Current workaround
```python
In [30]: s
Out[30]:
shape: (2,)
Series: '' [list[i64]]
[
        [1, 2, 3]
        [4, 5, 6]
]

In [31]: s.list.eval(pl.element().product()).list.first()
Out[31]:
shape: (2,)
Series: '' [i64]
[
        6
        120
]
```