Add support for reactive line charts for plotly

[nojaf]

📝 Summary

Similar to #7546, we also want Plotly line charts to be reactive.

(Also see #7733)

🔍 Description of Changes

📋 Checklist

• I have read the contributor guidelines.
• 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).
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

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Project	Deployment	Review	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jan 8, 2026 3:31pm

[Copilot]

Pull request overview

This pull request adds support for reactive line charts in Plotly, extending the existing reactive plot functionality that already supported scatter plots, heatmaps, treemaps, and sunburst charts. The implementation follows Altair's behavior by extracting all points within the x-range of a box selection, regardless of y-values.

Key Changes

• Added scatter/line point extraction functions (_extract_scatter_points_numpy and _extract_scatter_points_fallback) that filter points by x-range only
• Integrated scatter point extraction into the selection workflow via _append_scatter_points_to_selection
• Added comprehensive test coverage for line charts, including tests for pure lines, lines with markers, multiple traces, and edge cases

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
marimo/_plugins/ui/_impl/plotly.py	Added scatter/line point extraction functions and integrated them into the selection workflow, updated documentation to mention line chart support
tests/_plugins/ui/_impl/test_plotly.py	Added comprehensive test coverage for line chart functionality, updated existing tests to reflect new behavior where scatter selections extract all points in x-range
examples/third_party/plotly/line_chart.py	Added example demonstrating reactive line charts with simple lines, lines with markers, and multiple line traces

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