bus-bench: raw CAN over MQTT, measured on the car Orin

SocketCAN to yukart/can/raw and back, per frame or batched, with loss and
latency from the kernel timestamp. No loss at a saturated 500 kbit/s bus;
batched costs the broker ~1 % of a core. Report in docs/impl/reports.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

README.md

@@ -16,6 +16,7 @@ needed.
 | Binary | Installed as | Does |
 |---|---|---|
 | `recorder` | `yukart-recorder.service` | Raw CAN + GNSS to disk, in sessions, under a storage bound |
+| `bus-bench` | not installed: a test tool | Raw CAN over MQTT, measured: SocketCAN → `yukart/can/raw` → loss and latency ([report](docs/impl/reports/BUS-BENCH.md)) |
 | `orin-status` | `yukart-orin-status.service` | The Orin's health on the bus, once a second: temperatures, CPU/GPU load, memory, power, fan, WiFi/LTE/tablet links, UPS battery (`yukart/host/*`) |
 
 ```bash