feat: Add Lonboard example

[fabito]

📝 Summary

Add Duckdb + Lonboard example

🔍 Description of Changes

Add a simple "thirdy party" example showing Lonboard integration.
Unfortunately, the rendered Map does not include the expected Layers.
Using the exact same code in a Colab Notebook works fine.

I am not sure whether this is a Lonboard or Marimo issue.
I am not very familiar with Anywidgets but am happy to help troubleshooting.

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Please provide a link if applicable).
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

📜 Reviewers

@akshayka OR @mscolnick

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
marimo-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 25, 2025 9:44am
marimo-storybook	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 25, 2025 9:44am

[github-actions]

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[fabito]

I have read the CLA Document and I hereby sign the CLA

[fabito]

recheck