Add Testnet Post-Halving Block Test Vectors

[teor2345]

In #1091, we added block test vectors for each network upgrade transition.

The Testnet block subsidy halves on Testnet at block 1_116_000. We want to add post-halving Testnet test vectors around 13 October 2020, after the first halving. (The first Mainnet halving is at Canopy activation, so it is covered by #1099.)

Preconditions:

• The block subsidy has halved on Testnet (around 13 October 2020)
• Testnet is past the block reorg limit for the first halving (that is, 1_116_102 or later)

Software and Data Requirements:

• A syncronised zcashd testnet instance
• The zcash-cli RPC tool

Tasks:

• Add the hex-encoded data of testnet blocks 1_115_999, 1_116_000, and 1_116_001 to https://github.com/ZcashFoundation/zebra/tree/main/zebra-test/src/vectors/
• Add the hex-encoded data of the highest finalized testnet block to https://github.com/ZcashFoundation/zebra/tree/main/zebra-test/src/vectors/
  • Note: finalized blocks must be at least 100 blocks behind the tip height
• Add lazy_static refs for each of those blocks to https://github.com/ZcashFoundation/zebra/tree/main/zebra-test/src/vectors/block.rs
• Add the block refs to the testnet block list in https://github.com/ZcashFoundation/zebra/tree/main/zebra-test/src/vectors/block.rs
• Run the Zebra tests, and check that they pass

[teor2345]

This seems like a quick and easy way to improve our test coverage.

I don't know if any of our current code depends on anything that happens after the first halving, but adding these test vectors is one way to be sure.

[teor2345]

Since we've shifted the mandatory checkpoint to Canopy in #1898, we should probably add these test vectors soon.