Goals for dashcam-only merge

• Cleanup and optimize factoring together with MQB and upcoming MQBevo/MEB
• Checksum validation, split CRC functions because older messages use XOR and overlap with MQB
• Gearshift position from Getriebe_03.GE_Waehlhebel
• Door-open states (bus position may force a compromise here)

Future goals (may not happen in this PR)

• Replace ACC message with TSK message for engagement state
• Handle camera harness integration (currently only gateway)
• HCA timeout mitigation (same basic issue as VW PQ, same mitigation works)
• Fuzzy fingerprinting based on Porsche VIN format
• Research and handle apparent minor variances between Macan model-years
• Longitudinal control (long-term, might de-scope from this PR)