Updates stale Polars graph visualization

[bryangalindo]

This change updates the stale polars.png file to use the new graph visualization node shapes from #169.

Changes

We're updating the following file: examples/polars/polars.png

How I tested this

• Successfully ran unit tests locally using the following command in the root directory: pytest tests/
• Visually inspected new graph visualization .png to confirm it matches new node shapes.

Notes

N/A

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.