Function slice 

pub fn slice<D: Dimension>(
    a: &StringArray<D>,
    start: Option<isize>,
    stop: Option<isize>,
) -> FerrayResult<StringArray<D>>

Slice each element by character index — s[start..stop] with negative indices counting from the end (Python-style). None for either bound keeps the corresponding edge.

step is intentionally not supported here (numpy.strings.slice’s step parameter requires character-level reverse iteration that is non-trivial under multi-byte UTF-8). Pass two slice calls if you need [start:stop:step] behavior.

Errors

Returns an error if the internal array construction fails.