Function combine_n 

pub fn combine_n(paths: &[&Path], op: BooleanOp, opts: BoolOptions) -> Path

Convenience N-ary fold (M-BOOL.6 / AUT-167).

combine_n(&[a, b, c, d], op) is combine(combine(combine(a, b), c), d). Empty slice returns an empty Path; single-element slice returns that path unchanged.