[Python] How to select the longest string from a list of strings in polars?

How do I select the longest string from a list of strings in polars?

Example and expected output:

import polars as pl

df = pl.DataFrame({
"values": [
["the", "quickest", "brown", "fox"],
["jumps", "over", "the", "lazy", "dog"],
[]
]
})


┌──────────────────────────────┬────────────────┐
│ values ┆ longest_string │
│ --- ┆ --- │
│ list[str] ┆ str │
╞══════════════════════════════╪════════════════╡
│ ["the", "quickest", … "fox"] ┆ quickest │
│ ["jumps", "over", … "dog"] ┆ jumps │
│ [] ┆ null │
└──────────────────────────────┴────────────────┘


My use case is to select the longest overlapping match.

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