Add static rendering in MujocoVideoRecorder

[flferretti]

This PR will add a method in the MujocoVideoRecorder class to return images to be rendered in Python Notebooks.

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📚 Documentation preview 📚: https://jaxsim--85.org.readthedocs.build//85/

[diegoferigo]

The logic of the new method you drafted is already in MujocoVideoRecorder.render_frame, but in that case we do not return the rendered frame and instead append it to the stored frames that will be converted to a video.

What about unifying that logic? I mean:

• Modifying the following method to return a frame without appending to self.frames:

  def render_frame(self, camera_name: str | None = None) -> npt.NDArray:

• Adding a new method for rendering and appending:

  def record_frame(self, camera_name: str | None = None) -> None:
      frame = self.render_frame(camera_name=camera_name)
      self.frames.append(frame)

[diegoferigo]

Awesome, thanks!