Single step the viewer render?

Is there a recommend way to single step the viewer renderer?

In the example code snippet, I would like to grab input (ex: keyboard presses for direction) and update viewer frames. Currently, viewer.launch(env) blocks.

```
if __name__ == "__main__":

physics = mujoco.Physics.from_xml_path(MODEL_PATH_XML)
task = Xarm7()
env = control.Environment(
physics, task, time_limit=_TIME_LIMIT, control_timestep=_CONTROL_TIMESTEP
)

action_spec = env.action_spec()
time_step = env.reset()
viewer.launch(env)
```
An alternative is to encode the teleoperation input as a policy, however it's a bit unclear how that structure would look. Any example snippets would greatly appreciated!