Function faces 

pub fn faces(
    points: &ExactPoints,
    arrangement: &Arrangement,
    budget: &mut PairBudget,
    options: &ExecutionOptions,
) -> GeomResult<Faces>

Number the faces of the complement of arrangement.

Face 0 is the unbounded face. Bounded faces are numbered from 1, ascending by the smallest half-edge (2 * piece, plus one for the backward direction) of their boundary walk. With V vertices, E pieces and C connected components, the count F satisfies V - E + F = 1 + C.

Each containment decided between components counts one pair against budget; cancellation is checked per vertex. A component whose extreme vertex does not decide its outer contour is Degenerate.