Function find_bounding_faces 

pub fn find_bounding_faces(
    blocks: &[Block],
    outer_faces_records: &[FaceRecord],
    direction: &str,
    side: &str,
    tol_rel: Float,
    node_tol_xyz: Float,
) -> (Vec<FaceRecord>, Vec<FaceRecord>, Vec<Face>, Vec<Face>)

Identify outer faces on the extreme of the requested axis using BFS.

Arguments

• blocks - All blocks in the system.
• outer_faces_records - Optional pre-computed outer faces in record form.
• direction - Axis name ("x", "y", or "z").
• side - Requested side ("min", "max", or "both").
• tol_rel - Relative tolerance for plane selection.
• node_tol_xyz - Node matching tolerance for BFS linking.

Returns

Tuple containing serialized faces and raw face objects for the lower and upper planes.