Chrysler: Safety mode for Compact US Wide

[jyoung8607]

• [x] Fix issue with checksums/counters in RX checks
• [x] Optimize factoring/sharing between this and the existing Chrysler port
• [ ] ~~Exit from ALLOW_DEBUG~~ (to be done by comma after initial merge)
• [x] Look for a better PCM message
• [ ] ~~Accommodate torque ramp-down on disengage~~ (will do this in another PR)

[jyoung8607]

Releasing from draft, ready for review.

This is safety-complete, but driving experience isn't great because the CUSW steering rack will sometimes fault when being slammed down to zero torque instantly on disengage. Per our Discord conversation back in February, I'm working on something to allow torque to fall at MAX_RATE_DOWN when disengaging. It's going to be a tricky change to critical code. It deserves its own PR, and can't come in first due to CI coverage tests. I propose to bring CUSW safety in now, gated under ALLOW_DEBUG like we'd probably start with anyway, and come back for the disengagement fix.