Add custom control rate to bindings

[tomasz-lewicki]

Previously, we were using a fixed control rate of 500Hz. This PR allows us to configure a custom control rate in binding code like so:

config = unitree_interface.RobotConfig(
    robot_type=unitree_interface.RobotType.G1,
    message_type=unitree_interface.MessageType.HG,
    num_motors=29,
    name="G1_test",
    control_frequency_hz=50
)

self.unitree_interface = unitree_interface.create_robot_with_config(self.interface_str, config)

When no rate is provided, we fall back to 500Hz.