mazda: read invalidLkasSetting from camera intervention bits

[mzdnick]

Problem

• Lane keep off in the vehicle settings silently disables steering: the EPS echoes the request and applies none of it, no block, no fault.
• The old LANE_LINES == 0 check (CarState: add invalidLkasSetting commaai/opendbc#1325, "TODO: is this needed?") read zero in sustained stretches at road speed while steering was delivered. An unmarked road is not an invalid setting.

Fix

• CAM_SETTINGS (0x485) carries the setting: both intervention bits are set while lane keep is on; either bit clear raises invalidLkasSetting, keeping the existing alert and no-entry gate.
• Arrival is latched once and held values are read, no freshness window: an unsent CAM_SETTINGS decodes as zeros and must not read as off.

Validation

• affected: the setting-off capture holds both bits clear for the whole drive; the flag stays steady through silent cycles.
• affected: setting-on corpus, 3 cars, 95 min, 53k frames: both bits set on 100% of frames, including button-off drives.
• control: LANE_LINES-only zeroes no longer flag; a car that never sends CAM_SETTINGS reads valid. Both pinned by test.
• mazda tests: 546 pass; new tests pin the mapping, hold-through-silence, mixed bits, and the LANE_LINES regression.
• device test: toggling the lane assist setting shows the alert and clears it on re-enable; the dash LKAS button does not alert.

AI Usage

Disclaimer: GLM-5.3 by Z.ai was used to help develop, debug, and document this submission. All changes were reviewed and validated by me.