Wrap pythonrc.py logic in a setup()` function to prevent leaking variables

[arjxn-py]

This PR wraps the contents of pythonrc.py inside a setup() function to avoid polluting the variables panel of jupyterlab debugger when launched from VS Code and this extension is installed.

Context

When JupyterLab is launched from VS Code, the debugger’s Globals panel becomes cluttered with variables injected from the VS Code Python extension’s pythonrc.py. Examples include original_ps1, is_wsl, result, and other internal helper variables. These show up as top-level globals in Jupyter kernels, making the debugger view noisy.

This change potentially reduces unwanted side effects for external tools (e.g., JupyterLab) while keeping functionality intact.

[arjxn-py]

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