Allow logged metrics as x-axis choices

[abidlabs]

• Passes discovered metric columns from the Metrics page through App into the Sidebar component
• The x-axis dropdown now lists all logged numeric metrics in addition to "step" and "time"
• The dataProcessing.js layer already supported arbitrary x-axis fields — this just wires the UI

Closes #466

[gradio-pr-bot]

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[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
trackio	minor

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• Allow logged metrics as x-axis choices

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[HuggingFaceDocBuilderDev]

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Install Trackio from this PR (includes built frontend)

pip install "https://huggingface.co/buckets/trackio/trackio-wheels/resolve/0e4f88a0cfc01e2b866743f9b5c880daa9ac185c/trackio-0.20.2-py3-none-any.whl"

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[abidlabs]

Once CI is green, I'll merge in this small PR (just a UI tweak and some changes to the tests to make them more robust) so that we avoid conflicts. Won't release just yet