Function verify_connectivity 

pub fn verify_connectivity(
    blocks: &[Block],
    face_matches: &[FaceMatch],
    tol: Float,
) -> (Vec<FaceMatch>, Vec<FaceMatch>)

For each face match:

1. GCD-reduce blocks and scale indices.
2. Extract both faces as canonical 2D grids.
3. Try stored permutation_index first (if available).
4. Fall back to try_all_permutations if needed.
5. On success, update the FaceMatch with the correct permutation_index.

Returns

(verified, mismatched) vectors of face matches.