chore(deps): pin librustzcash crates to NU6.3 testnet-supporting pre-release version.

[nuttycom]

Motivation

Track upstream librustzcash development by pinning Zebra's zcash_* dependencies to librustzcash release/nu6.3_testnet_support branch, ahead of the next round of crate releases.

The [patch.crates-io] entries are temporary — they point at a librustzcash git revision and must be
replaced with published crate versions before the target branch is released.

Solution

• Add [patch.crates-io] directives pinning equihash, f4jumble,
  transparent (zcash_transparent), zcash_address, zcash_encoding,
  zcash_history, zcash_keys, zcash_primitives, zcash_proofs, and
  zcash_protocol to the librustzcash release/nu6.3_testnet_support branch
  (rev 703fe3e6608fab8be0dedbbcbf684f030a1ea451).
• Update the miner-reward transaction builders in
  zebra-rpc/src/methods/types/transaction.rs for the removed lifetime
  parameter on zcash_primitives' transaction Builder — it is now
  Builder<P, U> instead of Builder<'a, P, U>, so the closure type
  annotations change from Builder<'_, _, _> to Builder<_, _>.
• Remove the zcash_unstable=nu6.3 config gate.

Tests

• CXXFLAGS="-include cstdint" cargo check --workspace --all-targets passes
  cleanly (0 errors).
• Full cargo clippy -D warnings and cargo test / nextest CI have not
  yet been run — see Follow-up Work.

Specifications & References

• librustzcash release/nu6.3_testnet_support: https://github.com/zcash/librustzcash
  (rev 703fe3e6608fab8be0dedbbcbf684f030a1ea451)

Follow-up Work

• Replace the temporary [patch.crates-io] git pins with published crate
  releases before taking this out of draft.
• Run the full cargo clippy -D warnings and cargo test / nextest CI
  suites and add a CHANGELOG.md entry if the final version is user-visible.

AI Disclosure

• No AI tools were used in this PR
• AI tools were used: Claude Code — fixed the compilation error caused by
  the Builder lifetime change and drafted this PR description.

PR Checklist

• The PR title follows conventional commits format: type(scope): description
• The PR follows the contribution guidelines.
• This change was discussed in an issue or with the team beforehand. (Opened as a draft; coordinating directly with maintainers, no tracking issue yet.)
• The solution is tested. (cargo check only so far — see Tests / Follow-up.)
• The documentation and changelogs are up to date. (Deferred until the dependencies are on published versions — see Follow-up.)

[Copilot]

Pull request overview

This PR is titled as a dependency-pinning chore — pointing Zebra's zcash_* dependencies at a librustzcash git revision ahead of the next crate releases — plus a small transaction Builder lifetime-annotation fix. In practice, the diff is far broader: it lands an experimental NU6.3 / "Ironwood" shielded pool and v6 transaction implementation across zebra-chain, zebra-consensus, zebra-state, zebra-rpc, zebra-network, and their tests/snapshots, while removing the tx_v6 feature gate (making Transaction::V6 unconditional) and dropping ZIP-233 handling. The PR is explicitly marked "Draft / not for merge as-is" with temporary [patch.crates-io] git pins.

Changes:

• Add temporary [patch.crates-io] git pins for the zcash_*/equihash/f4jumble/transparent crates and bump workspace pre-release versions; update coinbase builders for the removed Builder lifetime parameter.
• Introduce the Ironwood pool and v6 transaction support: new ironwood types, value-balance pool, DB column families + migration (DB format 27 → 28), consensus rules, three-era Halo2 verifier routing, and NU6.3 network upgrade.
• Remove the tx_v6 feature and ZIP-233 (zip233_amount) handling from serialization, RPC coinbase construction, and fee/miner-reward paths; expand RPC valuePools from 5 to 6 entries.

Risk scan / holistic assessment:

• BLOCKER (process/consensus): This is consensus-critical code (serialization, verification, DB format, network protocol versions). It uses placeholder consensus branch IDs and provisional protocol versions, temporary git patches, and per the description has not had cargo clippy -D warnings or the full test suite run. It is not mergeable as-is and needs full human review.
• IMPORTANT (discrepancy): The PR description understates scope and cites a different librustzcash revision (8a0ae65…) than the one actually committed (703fe3e…, referencing PR #2509, not main). Flagged inline on Cargo.toml.
• Positive: The Ironwood/NU6.3 logic I inspected is internally consistent — the transaction accessors, three-era Halo2 verifier routing, value-balance widening to 48 bytes, and the new consensus rules all line up, and the new consensus checks have unit tests in zebra-consensus/src/transaction/tests.rs.

Reviewed changes

Copilot reviewed 24 out of 25 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Cargo.toml	Adds temporary [patch.crates-io] git pins and pre-release version bumps; rev/scope differs from PR description.
zebrad/Cargo.toml, zebra-test/Cargo.toml	Remove the tx_v6 feature definitions.
zebrad/tests/integration/regtest.rs	Renames the nu7/tx_v6-gated block-template test to an unconditional nu6_3 test and drops the zip233_amount argument.
zebrad/src/components/mempool/tests/vector.rs	Inserts an nu6_3 activation height into the mempool network-upgrade test.
zebrad/src/components/mempool/storage/tests/prop.rs	Removes tx_v6 cfg gates; unwraps/rewraps ShieldedDataV6 to reuse the Orchard conflict filter.
zebra-state/src/tests.rs	Removes the tx_v6 cfg gate from the Transaction::V6 match arm.
zebra-state/.../non_finalized_state/tests/{vectors,prop}.rs	Thread an extra Default::default() Ironwood tree into Chain::new and include the Ironwood note-commitment tree in comparisons.
NU6.3 / Ironwood implementation (broader diff: zebra-chain, zebra-consensus, zebra-state, zebra-rpc, zebra-network)	Adds the Ironwood pool, v6 transaction rules, DB migration/format bump, Halo2 verifier eras, and RPC value-pool expansion supporting the new upgrade.

[dannywillems]

utACK 6ac219f

[conradoplg]

Merging (into nu63-ironwood) per discussion to test this in CI