fix: recover typed node rejections on every JSON-RPC method

[zancas]

Closes #1407. Top of the #1404 follow-up stack — the base branch is test/1406-passthrough-contract-tests (PR #1410, which stacks on #1409 → #1405); retarget as the stack merges. Only the top commit belongs to this PR.

Problem

Only two of the 28 JSON-RPC methods recovered the node's typed rejection from the indexer error's source() chain: sendrawtransaction walked for the typed RpcError, and getblock recognized a single hard-coded transport case (HTTP 500 → "block not found"). The other 26 mapped every error through invalid_params_error_object, so a node rejection of, say, getrawtransaction or z_gettreestate reached the client as a generic invalid-params object — wrong code, no legacy error code, reason buried in a data string. This is the JSON-RPC face of the masking family from #1404, and an in-code comment acknowledged it: "Currently all errors are hidden from downstream client, a full fix should be implemented."

Fix

• error_object_from_source_chain (the shared walk skeleton) now takes its fallback as a parameter; internal_error_object is extracted alongside invalid_params_error_object.
• A new general translator, error_object_from_indexer_error, recovers the typed RpcError when the chain carries one and forwards its code and message. Otherwise it falls back to the exact invalid-params object the plain-delegation methods returned before — non-rejection errors keep their wire shape, so behavior changes only when a node rejection is present.
• All 26 plain-delegation sites now use the general translator. getblock keeps its zcashd-compatible "block not found" arm ahead of the generic recovery rather than instead of it. sendrawtransaction is behaviorally unchanged.
• The stale "temporary fix" comment is replaced with a description of the implemented design.

Tests (translator tests written first; the meaningful case confirmed red)

Before the fix, getblock_error_object_from_indexer_error masked a legacy-code -25 rejection as a -32603 internal error — that test was confirmed red, then green. Six tests now cover the three translators (recovery plus fallback pinning for each), built on a small nestable Wrap fixture: the translators consume only source() chains, so a minimal typed wrapper reproduces exactly what they see from production error types.

Verification

cargo fmt --all --check clean, cargo clippy --workspace --all-targets clean, and cargo nextest run on the production set green — 376/376, the prior 370 plus the six new translator tests.

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