Function find 

pub fn find<D: Dimension>(
    a: &StringArray<D>,
    sub: &str,
) -> FerrayResult<Array<i64, D>>

Find the lowest index of sub in each string element.

Returns an Array<i64, D> preserving the input shape, where each element is the index of the first occurrence of sub, or -1 if not found.

Errors

Returns an error if the internal array construction fails.