Handle psutil dependency on emscripten

[ObservedObserver]

Summary

• avoid installing psutil on emscripten targets so micropip can install pygwalker in JupyterLite

Testing

• not run (not requested)

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https://chatgpt.com/codex/tasks/task_e_690a9d90947883228cb7cc50e0cd3722

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[!NOTE] Make psutil optional on emscripten and harden nbconvert detection by safely reading the parent process cmdline.

• Utils / environment checks:
  • Safely import psutil with fallback to None when unavailable.
  • Add _get_parent_cmdline() with robust exception handling and use it in check_convert() to detect jupyter-nbconvert.
• Packaging:
  • Make psutil a conditional dependency (sys_platform != "emscripten") in pyproject.toml.

^{Written by Cursor Bugbot for commit 5100dc4b7e77adcd30847e529ad310008891d425. Configure here.}