Function face_interior_point_where 

pub fn face_interior_point_where<S: Scalar>(
    model: &Model<S>,
    face_id: FaceId,
    max_nodes: usize,
    epsilon: S,
    seed: u64,
    accept: impl FnMut(S, S) -> GeopResult<bool>,
) -> GeopResult<Option<(S, S)>>

Like face_interior_point, but for a caller that needs a point with some further property: up to one interior point per outer coedge (stepped in from it, in loop order) is handed to accept, and the first it accepts is returned. Ok(None) means interior points were found but none was accepted; an error, as for face_interior_point, that none was found.