Updates to digests and transaction format corresponding to recent changes to ZIPs

[vivek-arte]

There was a rearranging of the transaction format and the digests that took place in zcash/zips#1086 and zcash/zips#1088.

This PR makes the changes to the test vectors to match them back to the spec.

[PaulLaux]

for orchard_zsa_digest(tx): I think we need 64-bit signed little-endian
digest.update(struct.pack('<q', tx.valueBalanceOrchard)) (small <q)

Also for orchard_zsa_action_groups_auth_digest(tx): I think we need the size.

           digest.update(write_compact_size(len(ag.proofsOrchard)))

           digest.update(bytes(ag.proofsOrchard))

Please verify.

[ConstanceBeguier]

About orchard_zsa_action_groups_auth_digest, I think proof compact size is not included into the digest according to ZIP 246 and ZIP 230.
According to ZIP 246, we have to add proofsOrchard into the digest.
According to ZIP 230, proofsOrchard contains only the proof and not the compact size.

[ConstanceBeguier]

About valueBalanceOrchard, I replaced Q by q in transaction encoding and digest evaluation.

[ConstanceBeguier]

About orchard_zsa_action_groups_auth_digest, I think proof compact size is not included into the digest according to ZIP 246 and ZIP 230. According to ZIP 246, we have to add proofsOrchard into the digest. According to ZIP 230, proofsOrchard contains only the proof and not the compact size.

I asked the ECC team for some clarifications about the evaluation of orchard_auth_digest.
If we need to update this digest,

1. we will also need to update it in Orchard repo
2. the modification in zcash-test-vectors must be done in a separate PRs to keep the same PR order across all repos