Fix CleanRL Advanced PPO video recording by replacing RecordVideo with custom RGB recorder

[virgilt]

Description

This PR fixes the broken --capture-video option in the CleanRL Advanced PPO tutorial (tutorials/CleanRL/cleanrl_advanced.py). The original implementation attempted to use Gymnasium’s RecordVideo wrapper, which does not support PettingZoo’s parallel environments or SuperSuit’s vectorized wrappers. As a result, enabling --capture-video always produced an exception or silently failed.

This PR replaces the unsupported wrapper with a post-training video recorder that:

• Creates a fresh, non-vectorized Atari environment with render_mode="rgb_array"
• Replays the trained policy for a configurable number of frames
• Captures RGB frames and writes an MP4 using imageio
• Saves the video inside the same TensorBoard run directory for easy experiment tracking

This restores full video-recording functionality for the tutorial and provides a more reliable, backend-agnostic way to generate videos of trained PettingZoo agents.

Additional changes

• Added imageio and imageio-ffmpeg to the tutorial requirements.txt since MP4 writing requires them.
• Added a small message clarifying why RecordVideo is disabled for vectorized multi-agent environments.

Fixes # (issue), Depends on # (pull request)
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Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

Screenshots

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Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have run pytest -v and no errors are present.
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I solved any possible warnings that pytest -v has generated that are related to my code to the best of my knowledge.
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes