An actuator that uses a PCA9685 controller to drive a servo.

Configuration is derived from the joint's motor_profile injected by BB.Actuator.Server:

• Position limits from motor_profile.motor_lower / motor_upper
• Velocity limit from motor_profile.motor_velocity_limit
• PWM range maps linearly to the motor's position range (motor_lower → min_pulse, motor_upper → max_pulse)

When a position command is received, the actuator:

1. Clamps the position to motor limits
2. Converts to PWM pulse width
3. Sends PWM command to the PCA9685 controller
4. Publishes a BB.Message.Actuator.BeginMotion via BB.Actuator.publish_begin_motion/3 (which handles the motor → joint-space conversion)

Example DSL Usage

controller :pca9685, {BB.Servo.PCA9685.Controller, bus: "i2c-1", address: 0x40}

joint :shoulder, type: :revolute do
  limit lower: ~u(-45 degree), upper: ~u(45 degree), velocity: ~u(60 degree_per_second)

  actuator :servo, {BB.Servo.PCA9685.Actuator, channel: 0, controller: :pca9685}
  sensor :feedback, {BB.Sensor.OpenLoopPositionEstimator, actuator: :servo}
end