Add final sapling root test vectors

[teor2345]

Motivation

In #2227, we need final sapling roots to test the chain history integration.

API Specifications

This PR contains data from zcashd's z_gettreestate RPC:
https://zcash-rpc.github.io/z_gettreestate.html

Solution

Add test vectors:

• Add final sapling root test vectors for mainnet and testnet
  • zcashd RPC returns the final sapling roots in big-endian order, but we want them in block order
• Add a test to make sure each block test vector has a final sapling root test vector
• Add tests to catch common mistakes
• Tidy some formatting and imports

Fix and test block header commitments:

• Ignore pre-sapling block commitments
  • Previously Zebra expected this variant to be all-zeroes
• Add structural and semantic validation tests for block commitment parsing

Review

@conradoplg is waiting on these test vectors for #2227.

Reviewer Checklist

• Test vectors are correct (partial tests in ZIP-221: integrate MMR tree from librustcash (without Orchard) #2227 and Implement incremental, sparse note commitment trees for Sapling and Orchard #1287)
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

Implement and test final sapling roots in Zebra #1287

[dconnolly]

🎉

[teor2345]

I've made the following changes to this PR:

• Reverse final sapling root byte order
  • zcashd RPC returns the final sapling roots in big-endian order, but we want them in block order
• Ignore pre-sapling block commitments
  • Previously Zebra expected this variant to be all-zeroes
• Add structural and semantic validation tests for block commitment parsing

@conradoplg feel free to approve and merge this PR so you can keep on going with #2227.

[conradoplg]

It works with the code from #2227 😁