Fix dotted metric names in line plots

[abidlabs]

Fixes #677.

Summary

• Escape Vega field-path metacharacters in dynamic line-plot encodings.
• Preserve the original labels while using escaped field references for axes, series, and tooltips.
• Add regression coverage for dots, brackets, and backslashes.

Verification

• cd trackio/frontend && npm test
• cd trackio/frontend && npm run lint
• cd trackio/frontend && npm run build
• cd trackio/frontend && node repro_issue_677_vega.mjs

Minimal reproduction

import math
import trackio

metric = "profiling/Time taken: GRPOTrainer.compute_loss"
trackio.init(project="issue-677-dotted-metric", name="trl-grpo-profile")
for step in range(12):
    trackio.log({metric: 0.25 + 0.08 * math.sin(step / 2)}, step=step)
trackio.finish()
trackio.show(project="issue-677-dotted-metric")

The reproduction files are intentionally untracked and were not committed.

[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
🦄	Changes	detected!	Details

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
trackio	minor

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• Fix dotted metric names in line plots

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[abidlabs]

Before / after Spaces

• Before fix — latest released Trackio
• After fix — preview wheel from this PR

Space	Expected result
Before	profiling/reference_metric renders; profiling/Time taken: GRPOTrainer.compute_loss is empty
After	Both profiling metrics render

Both Spaces use byte-identical app.py files and serve the same 12 values for each metric. The after Space serves the exact frontend bundle built from this branch.

[qgallouedec]

Not a trackio expert but this looks right to me. I checked escapeVegaField against vega-util's splitAccessPath and it round-trips profiling/Time taken: GRPOTrainer.compute_loss back to the literal key, and every field: in the spec looks covered.

One thing I wasn't sure about: quotes aren't escaped. splitAccessPath seems to enter quote mode whenever i === b, which for a field with no dots holds at every position, so something like say "hi" would still break. vega-lite's replacePathInField uses /(\[|\]|\.|'|")/g. Might be worth the union, though it doesn't affect us, our metric names come from Python identifiers.

Thanks for the quick turnaround.

[abidlabs]

Thanks for catching that @qgallouedec! Addressed now.