Type is missing when constructing a list from struct with a datetime field

[hustxiaoc]

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

use polars::prelude::*;

fn main() {
    let a = Series::new("a", vec![1715075144098_i64; 10]);
    let b = Series::new("b", vec!["1"; 10]);
    let aa = a.i64().cloned().unwrap().into_datetime(TimeUnit::Milliseconds, None).into_series();

    let s = StructChunked::new("s", &vec![aa, b]).unwrap().into_series();
    let mut aa = vec![];
    for i in 1..9 {
        aa.push(s.slice(0, i));
    }
    let ss = Series::new("name", aa);
    dbg!(&ss.dtype());
}

Log output

[src/main.rs:14] &ss.dtype() = List(
    Struct(
        [
            Field {
                name: "a",
                dtype: Int64,
            },
            Field {
                name: "b",
                dtype: String,
            },
        ],
    ),
)

Issue description

Type datetime is lost

Expected behavior

List(
    Struct(
        [
            Field {
                name: "a",
                dtype: Datetime(
                    Milliseconds,
                    None,
                ),
            },
            Field {
                name: "b",
                dtype: String,
            },
        ],
    ),
)

Installed versions

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