📝 Use PyGraphviz for documentation diagrams

[denialhaag]

Description

🤖 AI text below 🤖

Render documentation diagrams with PyGraphviz 2 or later, whose wheels bundle Graphviz, and remove the system Graphviz package from Read the Docs.

Use temporary to_svg(dd, ...) helpers to keep SVG export calls to one line until the minimum MQT Core version includes PyGraphviz-backed SVG export. Their removal is tracked in #1013.

AI notice

This PR and its contents were created with the assistance of GPT-6 Astra via Codex.

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

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[burgholzer]

Just an idea 😌

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
python/mqt/ddsim/utils.py	0.0%	5 Missing ⚠️

📢 Thoughts on this report? Let us know!

[burgholzer]

LGTM 👍🏻