test(rpc): cover BatchSizeLimitMiddleware with max_entries=0

[Kewe63]

Summary

BatchSizeLimitMiddleware accepts a max_entries: usize and rejects any batch whose length exceeds it. The CLI value parser parse_max_batch_entries rejects 0 with must be >= 1, so the runtime cap is always at least 1. However, the in-process BatchSizeLimitMiddleware::new constructor has no such guard — callers can intentionally build a "no batches allowed" layer with max_entries = 0, and the middleware must behave sensibly in that case.

This corner case had no test coverage.

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Fix

Added a focused test locking in the documented behavior for max_entries = 0:

• Any non-empty batch is rejected with BATCH_TOO_LARGE_ERROR_CODE, and the error message names the offending size and limit.
• Empty batches are deliberately not asserted on: MockRpcService rejects empty batches with a different error code (-32600 "Invalid request"), and pinning the middleware's response shape on top of that quirk would lock in the wrong contract. The empty-batch case is left to the JSON-RPC layer below the middleware.

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Changes

File: crates/arc-evm-node/src/ (batch size limit tests)

• Added batch_size_limit_max_entries_zero test covering the max_entries = 0 case with non-empty batch inputs.

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How to Test

# Batch size limit tests
cargo test -p arc-evm-node --lib batch_size_limit
# ✅ 7 passed, 0 failed

# Format & lint
cargo fmt --check -p arc-evm-node
cargo clippy -p arc-evm-node --tests -- -D warnings
# ✅ Both clean

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Risk & Impact

None. Test-only addition — no production code modified. Locks in correct middleware behavior for an untested constructor edge case.

Type: 🧪 Test coverage