Feat/coinbase pay to contract

[jcnelson]

EDIT: this PR now supports building coinbase transactions that pay to either a smart contract or an alternative standard principal. The latter permits the miner to pay to a cold storage address automatically.

This PR implements #3101 by altering the TransactionPayload::Coinbase(..) type variant to include an optional smart contract address alternative recipient address, be it a contract or standard principal address. If given, the encoded transaction payload will have ID 0x05, and will include a serialized smart contract identifier principal. When processed in epoch 2.1, the block reward will be transferred to this smart contract address instead of the miner. In addition, I have updated the node software to accept a pay_to_contract contract contract or standard address under the [miner] heading called block_reward_address, which if given, will cause the node to create pay-to-contract alternative recipient coinbases for blocks mined after epoch 2.1 (the node ignores this field in epoch 2.05 and earlier).

I have added test coverage for:

• the new transaction encoding
• the static transaction validation tests (which are now epoch-gated to check for this new variant)
• the account crediting logic
• the miner's ability to produce a valid history of blocks that pay to a smart contract OR standard principal
• the relayer's ability to reject pay-to-contract OR pay-to-alt-principal blocks that are mined before epoch 2.1
• the node's ability to mine pay-to-contract OR pay-to-alt-principal blocks only once epoch 2.1 goes live

The code includes the relevant feature gating to ensure that a pay-to-contract pay-to-alt-principal block can only be successfully preprocessed in epoch 2.1. This prevents a Stacks 2.1-series node from accepting a pay-to-contract pay-to-alt-principal block at all before epoch 2.1 goes live. But, this differs slightly from how a 2.05-series node will handle such a block -- the 2.05-series node will not even be able to decode it, thereby making any attempt to push such a block to it fail with either an HTTP 400 (if sent via HTTP) or a temporary ban (if sent via p2p). I can make the 2.1-series node just as strict by adding feature gates to the p2p and HTTP endpoints, but I'm not sure it will make an appreciable difference in safety. Also, I'm not sure it's a good idea to make 2.1-series nodes ban each other for this, since if it turns out there's an off-by-one error somewhere in the gating logic that causes nodes to produce these blocks before they're supported, the nodes could accidentally all ban each other, leading to a catastrophic network partition. Open to feedback on this.

[codecov]

Codecov Report

Merging #3164 (e8c85f8) into next (00ca64b) will decrease coverage by 0.41%.
The diff coverage is 89.81%.

❗ Current head e8c85f8 differs from pull request most recent head 6376520. Consider uploading reports for the commit 6376520 to get more accurate results

@@            Coverage Diff             @@
##             next    #3164      +/-   ##
==========================================
- Coverage   84.19%   83.78%   -0.42%     
==========================================
  Files         268      268              
  Lines      212573   213534     +961     
==========================================
- Hits       178981   178902      -79     
- Misses      33592    34632    +1040     

Impacted Files	Coverage Δ
clarity/src/vm/docs/mod.rs	86.30% <ø> (ø)
src/chainstate/stacks/db/mod.rs	87.26% <ø> (ø)
src/cost_estimates/fee_medians.rs	93.27% <ø> (ø)
src/cost_estimates/fee_scalar.rs	90.78% <ø> (ø)
src/main.rs	0.08% <0.00%> (ø)
src/net/download.rs	32.43% <0.00%> (-8.74%)	⬇️
src/net/rpc.rs	31.50% <0.00%> (-0.21%)	⬇️
testnet/stacks-node/src/tests/epoch_21.rs	90.85% <19.67%> (-5.84%)	⬇️
testnet/stacks-node/src/config.rs	56.02% <20.00%> (-0.25%)	⬇️
src/chainstate/stacks/auth.rs	97.82% <80.00%> (-0.03%)	⬇️
... and 64 more

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[pavitthrap]

lgtm!

[kantai]

LGTM!

[jcnelson]

Thanks for the approvals! Let's get #3180 merged to this PR, and then I'll merge this all into next.

[blockstack-devops]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.