test(state, rpc): handle coinbase Sapling spends in proptests broken by #10527

[upbqdn]

Motivation

Several CI jobs are red on main:

1. Five proptests in zebra-rpc::methods::tests::prop fail after fix(chain): reject coinbase Sapling spends during deserialization #10527. The any::<Transaction>() (and any::<[Transaction; 2]>()) arbitrary strategies can produce coinbase transactions containing Sapling spends. After fix(chain): reject coinbase Sapling spends during deserialization #10527 those are rejected during deserialization, so send_raw_transaction returns a deserialization error before reaching the mempool, and each affected test waits indefinitely for a mempool request that never arrives.
2. Three proptests in zebra-state::service::finalized_state panic for the same reason: chains generated by PreparedChain contain coinbase transactions with Sapling shielded data that fail to round-trip through IntoDisk/FromDisk. roundtrip_transaction hits the same panic via any::<Transaction>().
3. Cargo.lock is out of date (missing the rand 0.8.5 → rand 0.8.6 bump for zebra-script).
4. cargo fmt --check fails.

#10527 updated the transaction_roundtrip proptest in zebra-chain for the same case but missed the downstream proptests that consume the same arbitrary strategy.

Solution

• Skip the invalid coinbase-with-Sapling-spends combination with
  prop_assume! in the five affected RPC proptests:
  • mempool_receives_raw_tx
  • mempool_errors_are_forwarded
  • rejected_txs_are_reported
  • rpc_queue_main_loop
  • rpc_queue_receives_all_txs_from_channel
• For zebra-state, fix the chain-builder fixup layer: clear
  sapling_shielded_data on coinbase transactions in
  fix_generated_transaction. This covers blocks_with_v5_transactions
  and all_upgrades_and_wrong_commitments_with_fake_activation_heights,
  which both build chains via PreparedChain.
• Add a prop_assume! to roundtrip_transaction since it bypasses the
  chain builder and uses any::<Transaction>() directly.
• The Transaction::Arbitrary strategy is intentionally left unchanged
  so the rejection path is still exercised by transaction_roundtrip
  and the GHSA-rgwx-8r98-p34c reproduction vector in zebra-chain (per
  the design choice in fix(chain): reject coinbase Sapling spends during deserialization #10527).
• Refresh Cargo.lock.
• Apply cargo fmt --all.

AI Disclosure

• AI tools were used: Claude (Opus 4) for investigation and patch drafting.

PR Checklist

• The PR title follows conventional commits format.
• The PR follows the contribution guidelines.
• This change was discussed in an issue or with the team beforehand. (Maintainer-driven: fixes CI breakage on main.)
• The solution is tested.
• The documentation and changelogs are up to date. (No changelog entry — test-only / build-only changes.)

[claude]

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[upbqdn]

Force-pushed. More proptests were failing than originally fixed.

[conradoplg]

Admin-merging due to stuck disconnects_from_misbehaving_peers