add(consensus): Adds block construction and validation for NU5 from block height 1 for Regtest

[arya2]

Motivation

We want to support Regtest in Zebra for integration testing.

Closes #8363.
Closes #8280.
Part of #7119.

This PR shouldn't change much, the regtest_nu5_activation_height field in the config should be removed, but that's a minor change.

Update: This PR shouldn't change anymore except to address review comments.

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Specifications

• ZIP 212
• Mean target difficulty on p. 132 of the spec:

MeanTarget(height ◦ N) :=
PoWLimit, if height ≤ PoWAveragingWindow
mean([ToTarget(nBits(𝑖)) for 𝑖 from height−PoWAveragingWindow up to height−1]),
otherwise.

• I couldn't find the POW_ADJUSTMENT_BLOCK_SPAN in the protocol spec, I don't think this should be a problem because there are always more than that many blocks where a check was replaced with relevant_chain.is_empty() by Canopy activation.

Update:
It's based on MedianTime and ActualTimespan in the specification, PoWAveragingWindow is also used in MeanTarget.

Solution

• Checks if the network is_regtest() in the start command, and if it is, commits the Regtest genesis block and skips starting the syncer
• Skips the ZIP 212 grace period for non-default networks
• Sets the mandatory checkpoint height at one block below Canopy activation for non-default networks (this may need some follow up changes, or changes in this PR)
• Adds funding streams and minimal protocol version for NetworkKind::Regtest
• Returns the reserved activation chain history root hash in the getblocktemplate method for blocks that should activate Heartwood network upgrade
• Checks Heartwood was activated at a given block height even if the current network upgrade is NU5
• Uses a slow start interval of Height(0) if PoW is disabled (this should be changed in a follow up PR or in this PR)
• Uses fewer than 11 blocks for calculating the median time past
• Uses fewer than 17 blocks for calculating the mean target difficulty

Testing

Added a test that gets block templates and submits them as blocks

Review

Anyone can review.

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• Does the PR scope match the ticket?
• Are there enough tests to make sure it works? Do the tests cover the PR motivation?
• Are all the PR blockers dealt with?
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Follow Up Work

• Some changes from Adds debug_validate_without_checkpoints field to testnet::Parameters and ignores the ZIP-212 grace period on Regtest #8428
• Adding a fields for:
  • Slow start interval
  • Disabling peer connections
  • Funding streams
  • Minimum protocol version
• Using zcash_address::Network instead of NetworkKind in transparent addresses?

[arya2]

Running full sync test here: https://github.com/ZcashFoundation/zebra/actions/runs/8904378011

Update:

Applied the correct slow start interval, cancelled the first full sync test, and running a new full sync test here: https://github.com/ZcashFoundation/zebra/actions/runs/8904708364

I'm also running one locally with checkpoint sync disabled on the lower-mandatory-checkpoint-height branch that's based on this branch.

[arya2]

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[mergify]

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