Go port of the read path of pybyd 0.0.75 (the client behind
jkaberg/hass-byd-vehicle): the bangcle white-box AES envelope, the
signing/checkcode layer, login, vehicle list, and realtime readings.
Scraping runs on a cron schedule rather than per Prometheus request
because each reading wakes the car's T-Box and drains the traction
battery; /metrics serves the last result.
Every numeric field of the realtime payload becomes a gauge, so the
exporter does not need a hand-maintained field list that goes stale
when BYD changes the payload.
Tests pin the wire format against pybyd byte-for-byte and drive the
client end to end against a fake cloud that speaks the real protocol.
Co-Authored-By: Claude Opus 5 <[email protected]>
