* refactor(eval): integrate preprocessor and postprocessor into rollout and eval_policy functions
- Updated the `rollout` and `eval_policy` functions to accept preprocessor and postprocessor parameters, enhancing the flexibility of the evaluation pipeline.
- Adjusted the implementation to apply preprocessing and postprocessing steps during policy evaluation, improving the overall data handling and processing flow.
* refactor(eval): remove redundant observation device conversion in rollout function
- Eliminated unnecessary device conversion for the observation dictionary within the `rollout` function, streamlining the code and enhancing readability.
- This change simplifies the observation handling process, aligning with the preference for clearer solutions.
* debug
* refactor(utils): enhance task handling in add_envs_task function
- Improved the `add_envs_task` function to validate the output of `task_description` and `task` calls, ensuring they return lists of strings.
- Removed the use of `else` statement for environments without language instructions, simplifying the logic and enhancing readability.
- Streamlined the observation dictionary handling by ensuring consistent data types for task attributes.
