feat: Add non-linear piecewise focus range to VisConfig sliders

[igorDykhta]

Adds focusRange and focusWeight options to VisConfigNumber sliders, allowing a configurable sub-range to occupy a disproportionately larger portion of the slider's physical width for finer control. Applied to heatmap intensity (0–1 range gets 60% of slider space out of the full 0–20 range). The slider splits into up to three zones (before, focus, after) with proportional width distribution.

Example: The heatmap intensity slider has a range of 0 to 20, but in practice, most useful adjustments happen between 0 and 1. With a linear slider, that entire 0–1 sweet spot occupies only 5% of the slider's pixel width — just a few pixels — making precise adjustments nearly impossible. This change lets the 0–1 range take up 40% of the slider, so users can fine-tune intensity without fighting the UI.

[Copilot]

Pull request overview

This PR introduces optional non-linear (piecewise-linear) scaling for numeric VisConfig sliders so a “focus” sub-range can occupy a larger fraction of the slider’s physical width, improving fine-grained control (applied to heatmap intensity).

Changes:

• Added slider-scale-utils (value↔position mapping + createSliderScale) and exported it from @kepler.gl/utils.
• Plumbed an optional scaleConfig through VisConfigSlider → RangeSlider → Slider to render/drag using the non-linear mapping.
• Added focusRange/focusWeight to VisConfigNumber and configured heatmap intensity to focus on [0.001, 1].

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/node/utils/slider-scale-utils-test.js	Adds unit tests for piecewise slider scale mapping and edge cases.
test/node/utils/index.js	Registers the new slider-scale utils test suite.
src/utils/src/slider-scale-utils.ts	Implements piecewise value↔position mapping and scale config creation.
src/utils/src/index.ts	Re-exports the new slider scale utilities from @kepler.gl/utils.
src/types/layers.d.ts	Extends VisConfigNumber with optional focusRange/focusWeight.
src/layers/src/heatmap-layer/heatmap-layer.ts	Applies focused slider scaling to heatmap intensity vis config.
src/components/src/side-panel/layer-panel/vis-config-slider.tsx	Generates and forwards scaleConfig from vis config settings.
src/components/src/common/slider/slider.tsx	Updates slider rendering/dragging to support optional non-linear scale config.
src/components/src/common/range-slider.tsx	Passes scaleConfig down into Slider.

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