fix: image dimensions for Altair PNG outputs

[daizutabi]

📝 Summary

This PR fixes a bug introduced in #9049.

Altair returns width and height metadata as float values for PNG. However, these values are used as the width and height attributes of an <img> element in the frontend. These attributes expect integer values.

Changes

• Cast width and height to int in the Altair formatter's _format_png_mimebundle function.

📋 Pre-Review Checklist

• 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).
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✅ Merge Checklist

• I have read the contributor guidelines.
• Documentation has been updated where applicable, including docstrings for API changes.
• Tests have been added for the changes made.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Apr 13, 2026 8:59am

[codecov]

Bundle Report

Bundle size has no change ✅

[Copilot]

Pull request overview

Fixes a regression in the Altair PNG formatter where PNG width/height metadata is emitted as floats, but consumed by the frontend as <img> attributes that require integers.

Changes:

• Cast Altair PNG metadata width/height to int when constructing the marimo MIME bundle.

[Light2Dark]

nice! thank you