fix: Allow list.contains() for list of categoricals

[c-peters]

fix #14559

Also a drive by fix for the List[categorical] <-> str where only the first value in the StringChunked was used:

df = pl.DataFrame(
    [(["a", "b"], "c"), (["a", "b"], "a")],
    schema={"li": pl.List(pl.Categorical), "x": pl.Categorical},
)
print(df.select(pl.col("li").list.contains(pl.col("x").cast(pl.Utf8))))
shape: (2, 1)
┌───────┐
│ li    │
│ ---   │
│ bool  │
╞═══════╡
│ false │
│ false │
└───────┘