Move functionality into blockchainsource, merge indexer services, unlock widespread mock based testing.

[idky137]

Moves all chain fetch in zaino-state behind the ValidatorConnector trait, making the whole crate mock testable.

• Splits ChainIndex into 2 separate traits: ChainIndex, ChainIndexRpcExt, keeping the core (zallet) API clean.
• Moves split chain fetch functionality (Zcash RPC vs ReadStateService) currently held in zaino-state::backends::{state, fetch} into BlockChainSource / ValidatorConnector.
• merges StateService and FetchService into unified NodeBackedIndexerService.

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Remaining work (not in this PR):

• update test vectors MockChainSource uses - currently the mock data held is insufficient to full test zaino state, the test data should be updated to a 1500 block chain containing transparent, sapling, orchard and ironwood transactions. (test vector builder code held in live-tests/e2e/tests/test_vectors.rs).
• Rewrite live-tests:
  • Regtest ValidatorConnector tests (full suite)
  • Regtest e2e tests (concise set)
  • MockchainSource crate / integration / unit tests (default test set).

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NOTE: This PR bcame much larger than I had anticipated, if it is too large to review / merge in its current form I am happy to divide it into several smaller PRS:

1. Split ChainIndex trait:

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2.n move StateService/FetchService functionality into ValidatorConnector:

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3. merge StateService and FetchService:

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[zancas]

The failing "Integration tests / Build zallet" checks are not caused by this PR. The zallet compile itself succeeds; the jobs die in a later workflow step, "Stage vendored db_dump", which looks for the db_dump helper that the zewif-zcashd build script vendors under zallet/target/.../build/zewif-zcashd-*/out/ and finds nothing.

The same step fails identically on unrelated zaino PRs (for example #1381, forty minutes earlier), and every zaino-interop-request run in zcash/integration-tests today is red the same way. The likely trigger is zallet's workspace-split restructure merged to main this morning (zcash/wallet #547–#549), which reworked the package layout and build paths so the workflow's hardcoded find pattern no longer matches where zewif-zcashd builds. The fix belongs in the zcash/integration-tests workflow; until it lands, this required check will stay red on every zaino PR.

[zancas]

A second CI-relevant finding, and this one is introduced by the PR (deterministic — reproduced twice in omnibus runs and once in isolation):

FAIL clientless::fetch_service zebrad::validation::z_validate_address
assertion `left == right` failed: mismatch for Sapling (zebrad passthrough via FetchService — keys omitted)
  left:  … diversifier: Some("977e0b930ee6c11e4d26f8"), diversified_transmission_key: Some("553ef2…") …
  right: … diversifier: None, diversified_transmission_key: None …

Cause. The test runs the shared suite with SaplingSuite::ZebradPassthroughFetchService (live-tests/clientless/tests/fetch_service.rs:721), which pins the old FetchService behavior: z_validate_address was a JSON-RPC passthrough to the validator, and zebrad's response omits diversifier and diversifiedtransmissionkey. The merged service changed that. At base, FetchService::z_validate_address called self.fetcher.z_validate_address(...); at the PR head, NodeBackedIndexerService::z_validate_address calls the local derivation crate::indexer::z_validate_address(address, &network) (packages/zaino-state/src/indexer/node_backed_indexer.rs:607-614) on both connection types, so the response now carries the derived keys and no longer matches the pinned None/None expectation.

Recommendation. Unify on the local computation — it matches the old StateService and zcashd, and the suite's "don't delegate component extraction to a remote actor" rationale does not apply to a local derivation. Concretely:

1. Switch the zebrad fetch test to SaplingSuite::Standard, and remove the now-unreachable ZebradPassthroughFetchService variant along with run_z_validate_sapling_zebrad_passthrough_fetchservice and its stale rationale comment (live-tests/clientless/src/lib.rs:121-150).
2. Keep the RPC marked deprecated: the merge silently dropped the tracing::warn!("{}", Z_VALIDATE_DEPRECATION) that the old FetchService emitted on every call (visible in the same hunk). Restore that warning in the merged implementation so operators keep the deprecation signal.