Cloning model collections should be performed in the registry

[Balint-H]

Hello,

I really like the environment implementations in playground, and it is good to see it maintained. @jamesheald and I are considering whether we could directly import the base classes and wrappers in other mjx environment suites (specifically for MyoSuite). However, with the current version of playground, the mujoco menagerie is cloned if MjxEnv is imported.

mujoco_playground/mujoco_playground/_src/mjx_env.py

Line 111 in 47c1f64

ensure_menagerie_exists() # Ensure menagerie exists when module is imported.

Would it be possible to move this check and download to, e.g., the registry scripts?

That way if we want to benefit from the maintenance and features from playground we can import them without triggering the downloading of large assets.

[btaba]

Hi @Balint-H , we'll look into this! Created a bug #126