test: confirm and fixture steering-wheel-heat command tags 70/71

[Bre77]

Intent

• Confirms and fixtures the two steering-wheel-heat command coordinates already declared in proto/command/car_server.proto: VehicleAction.autoStwHeatAction=70 (AutoStwHeatAction.on, bool) and VehicleAction.stwHeatLevelAction=71 (StwHeatLevelAction.stw_heat_level, enum Unknown=0/Off=1/Low=2/High=3).
  • Confirmed against Teslemetry's public python-tesla-fleet-api test suite (tests/test_ble_climate_commands.py), which documents both commands as live-attempted against a real test vehicle: the vehicle's ACK decodes correctly and returns the feature-specific rejection cabin comfort remote settings not enabled, rather than a parse failure - confirming the vehicle recognizes these exact field/tag/payload combinations. That repo's independent StwHeatLevels mapping (1/2/3 -> Off/Low/High) matches this repo's declaration.
  • No disagreement found; both fields match the checked-in declaration exactly, so this is confirmation-only - no proto edit, no changeset.
• Adds a language-neutral golden-payload fixture (fixtures/golden/steering_wheel_heat.json) covering tag-70 off/on and all four tag-71 enum values, with the outer Action.vehicleAction=2 wrapper tag identified alongside each case.
  • New test suites in both packages (packages/typescript/test/, node --test; packages/python/tests/, unittest) load the same fixture and assert both encoders produce byte-identical output and both decoders round-trip it back to the same values. Wired into ci.yml after each package's build step.
  • This is the project's first test suite for the generated packages themselves (previously only script-level unittest coverage existed); documented in AGENTS.md.
• Live-vehicle confirmation covers the off/on bool and the Low enum value; Unknown/Off/High share the same confirmed field/tag mapping and are exercised by the fixture's local encode/decode round-trip but weren't individually sent to the test vehicle.