HKG: HDA2 ALT_BUTTON support

[ccdunder]

Issues fixed:

1. CAN error on start prevents can becoming valid:

   "filename": "opendbc_repo/opendbc/can/parser.cc",
   "funcname": "UpdateValid",
   "levelnum": 40,
   "lineno": ' '230,
   "msg": "0x1CF \'CRUISE_BUTTONS\' NOT SEEN"}',
   

2. No resume from cruise standstill.

Testing:

• Updated safety tests.

Routes:

• See Car Port: Kia Carnival HEV 2025 (HDA2) openpilot#34246

Related:

• Car Port: Kia Carnival HEV 2025 (HDA2) opendbc#1580
• HKG: Car Port for Kia Carnival 2025 (HDA2) opendbc#1558

[ccdunder]

I think this is ready for review.

For the reviewer: at first glance, you will probably wonder "why refactor the tests just to add a test case?" I did this in order to handle the combinatorial nature of hyundai configs¹ in a balanced way — neither copy-pasting large chunks nor making test code so complex that it deserves its own tests. For reference, subaru and honda are using similar patterns (e.g. dedupe setUp and mixins). Totally open to your feedback on where to strike the balance or how, just wanted to provide context.

Footnotes

1. something like (buttons, alt-buttons) * (steering, alt-steering) * (ice, hybrid, ev accelerators) * (hda1 camera, hda1 radar, hda2). Many of which aren't covered today 👀 but that seems out of scope for this PR. ↩