feat(zcash): add transaction pages with shielded bundles and fee lookup

[MatiasOS]

Description

Adds the Zcash transactions list (/zec/txs) and transaction detail (/zec/tx/:filter) pages, plus their tzec equivalents.

The transaction page handles three things that make Zcash different from Bitcoin:

• Shielded bundles: Sapling spends and outputs, Orchard and Ironwood actions, and Sprout JoinSplits. Each bundle shows which way its value balance moved.
• Fully shielded transactions: when vin and vout are both empty, the page explains that amounts and parties are encrypted. It doesn't render empty input and output columns.
• Fees: computed from the transparent value balance: inputs, plus value leaving the shielded pools, minus outputs.
  • Zebra doesn't return the values of transparent inputs.
  • For transactions with transparent inputs, a "Look up input values" button fetches the previous transactions on demand, up to 10.

The transactions list pages client-side within a single block, which costs one getblock call. Newer/older block navigation works out the chain tip from the block's confirmations, so it needs no extra call.

Related Issue

Part of #398. Stacked on #408.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• Performance improvement
• Other (please describe):

Changes Made

• New components: ZcashTransactionsPage, ZcashTransactionPage, ZcashTransactionDisplay and ZcashShieldedBundles.
• A countPreviousTransactions util, with a unit test.
• A shared labels.ts holding the typed i18n keys for pools and transaction kinds. The existing dashboard and block components now use it too.
• Routes and lazy exports for zec|tzec/txs and zec|tzec/tx/:filter.
• zcash locale strings and tooltips.zcash.tx in all 5 locales.
• A hermetic e2e spec at e2e/tests/shared/mocked/zcash-transactions.spec.ts. The shared RPC mock now also serves transactions:
  • a synthetic transparent transaction
  • previous transactions for input lookups

Screenshots (if applicable)

Checked locally against mocked RPC data:

• a fully shielded transaction
• a transparent transaction after its input lookup
• the capped shielding transaction
• the transactions list
• a 400px-wide layout

Checklist

• I have run npm run format:fix and npm run lint:fix
• I have run npm run typecheck with no errors
• I have run tests with npm run test:run
• I have tested my changes locally
• I have updated documentation if needed
• My code follows the project's architecture patterns

Additional Notes

• Fees on real mainnet transactions:
  • 36a167f6…, which is Ironwood only: 0.0001 ZEC.
  • c973d2f1…, which uses Sapling and Ironwood: 0.0002 ZEC.
  • 717b54c3… has 15 transparent inputs, so the lookup stops at 10 and the page says so.
• Caching: when the persistent cache is enabled, resolved input values are cached with a confirmed transaction. A later visit shows the fee without new lookups.
• Tests:
  • npm run test:run: 151 passing.
  • Hermetic Zcash e2e specs: 9 passing.