bench(zenoh): Add performance benchmarks

[zhexuany]

Performance Task

Add benchmarks to measure Zenoh plugin throughput and latency.

Metrics to Track

1. Throughput: Messages/second per subscription
2. Latency: Message publish to callback delivery time
3. Memory: Memory usage per active subscription
4. CPU: CPU usage under load

Proposed Solution

Use Google Benchmark library to measure baseline performance and detect regressions.

Files to Add

• middlewares/zenoh/src/zenoh_plugin/bench/

Priority

Low - Performance is currently acceptable