Function split_label 

pub fn split_label(raw: &str) -> LabelParts

Split a raw label into center + traveling H + charge.

Accepts backend strings like NH2, OH, NH4+, O−, *, and marked forms $R_1$ / R^2 (markup stays on center for [parse_label_markup]). Bare underscores (my_name) are not treated as scripts at split time.