Add functionality to download training metrics graphs

[andersendsa]

Summary

• Implemented a "Download" button in the MetricGraph component to let users export training metrics graphs as PNG images.
• Extracted SVG elements natively, drew them on a canvas, and triggered a PNG download directly, without introducing extra dependencies.

Closes: #5656

How to test

1. Open the application UI and navigate to your project.
2. Click on the Models tab in the main navigation menu.
3. Select a trained model from the list to open the Model Details view.
4. Click on the Training Metrics tab inside the details panel.
5. You should see one or more line graphs (e.g., Training Loss, Validation Accuracy, etc.).
6. Look at the top-right corner of any graph's container box. You should now see a new Download icon button.
7. Click the Download button.
8. Verify Download: A .png file (named based on the graph's title, e.g., training_loss_metrics.png) should be downloaded to your local machine.
9. Verify Image Quality: Open the downloaded image file. Confirm that the graph is fully visible with a solid white background, and that all data lines, axes, and labels rendered correctly exactly as they appeared in the UI.

Checklist

• The PR title and description are clear and descriptive
• I have manually tested the changes
• All changes are covered by automated tests
• All related issues are linked to this PR (if applicable)
• Documentation has been updated (if applicable)

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[andersendsa]

Hi @dwesolow, @jpggvilaca, @A-Artemis pls let me know if this pr needs any changes or if it is good to merge