rpc: fix testing build block v1 according Hive Test

[lupin012]

This PR fixes the following Hive test failures:

• testing_buildBlockV1/build-block-empty-transactions
• testing_buildBlockV1/build-block-invalid-transaction
• testing_buildBlockV1/build-block-with-transactions

Note:
The test testing_buildBlockV1/build-block-from-mempool currently still fails; this is expected as it will be updated to a speconly type, following the changes in:
execution-apis PR #783.

Changes vs main

• Explicit transaction list support in testing_buildBlockV1
  In main the endpoint returns an error if a non-empty transaction list is passed. This branch implements the full flow: raw transactions are decoded, the sender is recovered via the chain signer, and nonces are validated sequentially per sender against the current state.
  Three modes: null → mempool, [] → empty block, [...] → exact transaction list with strict nonce check.

• execution/builder/parameters.go — added CustomTxnProvider txnprovider.TxnProvider: allows injecting an alternative transaction source without exposing the concrete type to the builder.

• execution/engineapi/testing_api.go

  • testingImpl now holds logger and db (kv.TemporalRoDB) to read account nonces from state.
  • staticTxnProvider (private) — yields the fixed transaction list exactly once, then returns nil.
  • The testing namespace is now wired into jsonrpc.APIList via node/eth/backend.go, consistent with all other namespaces.

  Tests — full coverage: input validation, busy execution paths, happy path (mempool and explicit list), nonce too high/low, multi-sender nonce tracking, fork-specific parameter propagation (Withdrawals, ParentBeaconBlockRoot) to assembleParams.

[Copilot]

Pull request overview

Fixes Hive failures for testing_buildBlockV1 by adding explicit transaction list support, wiring the testing_ namespace through the standard JSON-RPC API registry, and aligning payload JSON output with expectations.

Changes:

• Implement explicit transaction-list flow in testing_buildBlockV1 (decode txs, recover senders, strict per-sender sequential nonce validation) and plumb it into the builder via a CustomTxnProvider.
• Wire testing_ into jsonrpc.APIList and pass the entry from node/eth/backend.go (with a prominent production warning when enabled).
• Adjust Engine API JSON encoding for blockAccessList to omit empty values; expand/adjust tests around the new behaviors.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rpc/jsonrpc/daemon.go	Adds optional testing API entry wiring to the centralized API list and logs a warning when enabled.
node/eth/backend.go	Constructs/passes testing_ RPC entry into APIList instead of manually appending.
execution/engineapi/testing_api.go	Implements explicit tx list decoding + nonce checks, DB-backed nonce reads, staticTxnProvider, and blockValue/extraData handling tweaks.
execution/engineapi/testing_api_test.go	Adds coverage for invalid tx bytes, nonce too high/low, multi-sender tracking, params propagation, and staticTxnProvider.
execution/engineapi/engine_types/jsonrpc.go	Makes blockAccessList omit empty values in JSON.
execution/builder/parameters.go	Adds CustomTxnProvider to allow overriding the transaction source.
execution/builder/builder.go	Uses CustomTxnProvider when provided, otherwise defaults to the builder’s injected provider.
cmd/rpcdaemon/main.go	Updates APIList call signature (passes nil testing entry).
cmd/mcp/main.go	Updates APIList call signature (passes nil testing entry).

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[Copilot]

decodeTxnProvider calls getAccountNonce the first time it sees each sender, and getAccountNonce opens a new temporal DB transaction + SharedDomains every time. For large explicit tx lists with many senders this adds significant overhead. Consider opening the temporal tx/SharedDomains/state.Reader once per BuildBlockV1 call (or once per decodeTxnProvider call) and reading all needed nonces from that single reader, caching them in expectedNonce.

[Copilot]

Nonce mismatches are treated as rpc.CustomError with ErrCodeDefault (-32000). Since this is a request/parameter validation failure (like the decode/sender recovery paths just above), returning rpc.InvalidParamsError (or at least using -32602) would be more consistent and easier for clients/tests to classify as an input error.

Suggested change

	return nil, &rpc.CustomError{
	Code: rpc.ErrCodeDefault,
	Message: fmt.Sprintf("nonce too high: address %v, tx: %d state: %d", sender.Value(), got, want),
	}
	}
	if got < want {
	return nil, &rpc.CustomError{
	Code: rpc.ErrCodeDefault,
	Message: fmt.Sprintf("nonce too low: address %v, tx: %d state: %d", sender.Value(), got, want),
	}
	return nil, &rpc.InvalidParamsError{Message: fmt.Sprintf("nonce too high: address %v, tx: %d state: %d", sender.Value(), got, want)}
	}
	if got < want {
	return nil, &rpc.InvalidParamsError{Message: fmt.Sprintf("nonce too low: address %v, tx: %d state: %d", sender.Value(), got, want)}