bus-bench: decoder stand-in and mixed-load runs

Raw frames to four subscribers plus envelopes to five, at the car's rate and
at a full bus. Raw never suffered; envelope deliveries are the load, with the
knee near 40,000 deliveries/s.

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

README.md

@@ -16,7 +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)) |
+| `bus-bench` | not installed: a test tool | Raw CAN and decoded-signal load over MQTT, measured: loss, latency, broker CPU ([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