class_docstr: Partially observable variant of the Pendulum gym environment.
  
  https://github.com/Farama-Foundation/Gymnasium/blob/main/gymnasium/envs/
  classic_control/pendulum.py
  
  We delete the angular velocity component of the state, so that it
  can only be solved by a memory enhanced model (policy).
code: def step(self, action):
      next_obs, reward, done, truncated, info = super().step(action)
      # next_obs is [cos(theta), sin(theta), theta-dot (angular velocity)]
      return next_obs[:-1], reward, done, truncated, info
  
file_path: ray/python/ray/rllib/examples/env/stateless_pendulum.py
imports: from gymnasium.spaces import Box
  import numpy
  from gymnasium.envs.classic_control import PendulumEnv
label_desc: Use image node_id 2 for calling the StatelessPendulum obj's underlying member method code with example usage: obj.step(action) and returns: next_obs,  reward,  done,  truncated,  info