Add zoom-responsive styling for direct scatter points

[FarhanAliRaza]

Motivation

• Direct scatter markers are fixed in screen-space size and opacity which makes them either too faint when deeply zoomed or too noisy in overviews.
• The goal is to make markers interpolate size and opacity on the client during zoom so detail is legible without rebuilding or retransmitting large traces.

Description

• Added zoom_size_factor, zoom_opacity, and zoom_emphasis parameters to the fluent Figure.scatter API and the Reflex-style components.scatter factory and serialized them into trace style with sensible, fixed-style-compatible defaults.
• Client-side logic _pointZoomStyle was implemented in js/src/50_chartview.js to compute a logarithmic interpolation (from the initial view) for size and opacity, clamped at the configured zoom_emphasis.
• The computed sizeFactor and adjusted opacity are applied consistently across rendering paths including the full points shader, the simple points shader, hover emphasis, and the pick/detection path so rendering, hover, and picking stay aligned.
• Input validation and docs were added in python/xy/marks.py and python/xy/components.py, tests were added/updated to cover serialization and validation, and static JS bundles were rebuilt and committed.

Testing

• Ran unit tests: PYTHONPATH=python python -m pytest tests/test_scatter.py tests/test_components.py -q, all tests passed (156 passed).
• Rebuilt and verified JS bundles with node js/build.mjs and make js-check, which succeeded and reported fresh static bundles.
• Ran style/type/lint checks with PYTHONPATH=python ruff check python/xy/marks.py python/xy/components.py tests/test_scatter.py and git diff --check, both succeeded.

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Codex Task

Closes #88

[codspeed-hq]

Merging this PR will not alter performance

✅ 94 untouched benchmarks
⏩ 1 skipped benchmark¹

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_{Comparing codex/add-zoom-responsive-size-and-opacity-for-scatter-points (2e89941) with main (b283b10)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[Alek99]

Review findings:

• [P2] js/src/50_chartview.js:2261: y-only zoom never activates responsive styling because a finite x zoom of 1 wins the nullish-coalescing chain. Combine the applicable axis zoom factors instead.
• [P2] js/src/50_chartview.js:2432: hover emphasis uses scalar g.size, not the point's encoded size. Large size-channel points therefore get a smaller hover overlay than the rendered point.
• [P2] js/src/50_chartview.js:2311: zoom_opacity is applied to the fill but explicit point strokes retain base opacity. Apply the zoom-adjusted opacity to the outline while preserving stroke_opacity.