mazda: read invalidLkasSetting from the camera's intervention bits

[mzdnick]

Problem

• With lane keep switched off in the vehicle settings, the EPS echoes the steering request and applies none of it: no block, no fault. Nothing on the bus named the setting.
• LANE_LINES == 0 (CarState: add invalidLkasSetting commaai/opendbc#1325, left with a "TODO: is this needed?") is not needed. It reads zero in sustained stretches at road speed while steering is 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 and clear when it is off. Either bit clear raises invalidLkasSetting, keeping the existing alert and no-entry gate.
• Arrival is latched once and the parser's held values are read, no freshness window: the flag stays steady between arrivals and a car that never sends the message never reads as off. NaN default, outside canValid.

Validation

• affected: the menu-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 zero stretches no longer flag; pinned by test.
• control: a car that never sends CAM_SETTINGS reads valid; pinned by test.
• mazda tests: 546 Mazda tests pass; new tests pin the mapping, hold-through-silence, mixed bits, and the LANE_LINES regression.
• device test: validated feature works as intended; toggling Mazda lane assist setting displays an alert that clears immediately when re-enabled. LKAS toggle on dash unaffected, no alert with LKAS disabled.

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 a human.