change(consensus): Skip coinbase spend must be shielded check on Regtest

[arya2]

Motivation

This PR is not yet ready for review.

Coinbase outputs must be shielded when first spent on Mainnet and Testnet in zcashd, but not on Regtest when configured with a flag, we want to do the same in Zebra.

Closes #8478.

Solution

• Skips coinbase output maturity check on Regtest

Tests

Updates existing tests for immature coinbase output spends failing validation in the transaction verifier and state utxo check.

Follow Up Work

Add a field to testnet::Parameters for configuring whether the coinbase maturity rule should be checked or ignored on Regtest.

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.

[arya2]

This PR still needs some work and this isn't currently a priority.