docs: modernize py dependencies docs and example

[nitobuendia]

Fixes #31431

A more common approach to packaging Python package is leveraging pyproject.toml files and having a src directory (instead of a flat directory). This change intends to update the documentation and examples to match this way of packaging Python packages.

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[tvalentyn]

R: @tvalentyn

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[tvalentyn]

Closed and reopened to rerun the tests