[FEATURE] Expose PID class members for voltage alignment during mode switching

[zyy37]

Is your feature request related to a problem? Please describe.

class PIDController
{
...
protected:
    float error_prev; //!< last tracking error value
    float output_prev;  //!< last pid output value
    float integral_prev; //!< last integral component value
    unsigned long timestamp_prev; //!< Last execution timestamp
};

When the mode needs to be switched, in addition to aligning the angle and angular velocity, the voltage and other parameters also need to be aligned. It is hoped to expose these variables within the PID, such as error_prev, output_prev, integral_prev. Thank you.