Duplicated MjData in MujocoEnv and Robot

[Balint-H]

Hello,

The rework of the class structure and its simplification in recent updates was a great improvement. I noticed one thing that I think may not have been intentional but want to double check:

Both the MujocoEnv class and the Robot env class have their own MjData structure, but they are not kept in sync. So if you take actions in an environment, only the Robot's MjData is kept up to date (i.e., env.robot.mj_data), while env.mj_data is kept at the initial frame.

Was this intentionally kept separate? Or would it be better to have the two point to the same reference/kept in sync?

@Vittorio-Caggiano

[vikashplus]

robot class is a abstraction designed to cleanly separate an env from a robot (either simulated/ real hardware). You can read more about it here

If a existing sim is available, it can be directly passed to the robot class (see here)
If its not passed then a new sim is created (see here)