Reduce Mutexed Global Variables for cold paths of brake state

[jr1221]

Description

Less commonly checked variables, like brake state, aren't worth a whole API to acquire a mutex, set a brake state, and then release every 10ms.

Acceptance Criteria

Use a read_brake_state command.

Proposed Solution

To make this better, just get the brake state via the PDU API. Since get is infrequent this performance hit of i2c will be commutatively less than calling mutexes in the brake loop.