[Test🧪] Add no-op branch tests for ZoneRouteRPCHook

[mxsm]

Prerequisites

• I have searched existing test issues

Test Scope

Module: zone-aware topic route filtering
File: rocketmq-namesrv/src/route/zone_route_rpc_hook.rs
Coverage: the existing tests cover successful filtering and JSON encoding; add low-risk branch coverage for requests and responses that should not be modified.

Test Cases

• Non-GetRouteinfoByTopic request leaves the response body unchanged.
• Non-success response leaves the response body unchanged.
• Missing or false zoneMode leaves the response body unchanged.
• Missing or empty zoneName leaves the response body unchanged.
• Zone matching remains case-insensitive for filter_by_zone_name.
• Validate with cargo test -p rocketmq-namesrv zone_route_rpc_hook.

Willing to contribute?

• I can submit a PR for this