fix: VID ADVZ check consistency of multiplicity in verify_share

[ggutoski]

closes: #644

This PR:

• do not panic for index out of bounds. Instead return Internal error.
• add check for consistency of multiplicity. Return Argument error instead of Internal error when multiplicity is inconsistent.
• Move tests from advz.rs to advz/test.rs. The only actual change to tests is the addition of a new test verify_share_with_different_multiplicity.
• @akonring do you know what's up with these TODOs?
  • https://github.com/EspressoSystems/jellyfish/blob/e18f3bc658a12de5f71cc35a1716c4766eae341a/vid/src/advz.rs#L535
  • https://github.com/EspressoSystems/jellyfish/blob/e18f3bc658a12de5f71cc35a1716c4766eae341a/vid/src/advz.rs#L914

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[akonring]

• @akonring do you know what's up with these TODOs?

  • https://github.com/EspressoSystems/jellyfish/blob/e18f3bc658a12de5f71cc35a1716c4766eae341a/vid/src/advz.rs#L535
  • https://github.com/EspressoSystems/jellyfish/blob/e18f3bc658a12de5f71cc35a1716c4766eae341a/vid/src/advz.rs#L914

Yes, I believe I put those comments there because we don't actually 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.

My memory fails my as to why I did not implement this check in the first place. At that point we were considering "batching" the KZG evals which might be the reason that the implementation was postponed.

Created an issue here: https://github.com/EspressoSystems/jellyfish/issues/654. Feel free to modify.