VID: verify consistency with the merkle root for all the evaluations in a VID share

[akonring]

Discussion of issue here: #653 (comment)

We don't check consistency with the merkle root for all the evaluations in a share (with multiplicity). The share only contains the merkle path for the first evaluation.

If we consider doing KZG eval batching in the future, we should represent the VID share such that consistency check with the merkle root can be done for all evaluations still.