Fix Slider property update freezing UI

[hannahblair]

Summary

• Fixes UI freeze when updating Slider properties (visibility, min/max/value) via gr.update() or gr.Slider() constructor in callbacks
• Root cause: The $effect that synced range_input.value directly conflicted with Svelte's bind:value — when min/max changed simultaneously with value, the browser clamped to stale bounds, causing a reactive loop
• Three targeted fixes in js/slider/Index.svelte:
  1. Removed redundant range_input.value set (already handled by bind:value)
  2. Made range_input reactive ($state) with null guard so the CSS progress effect works correctly when visibility toggles
  3. Wrapped old_value write in untrack() to prevent unnecessary effect re-runs
  4. Reordered range input attributes so min/max/step are set before bind:value

Closes #12995

Test plan

• Run pnpm vitest run js/slider/ — unit tests pass
• Verify with reproduction scripts from Slider property update freezes UI in Gradio ≥6.6.0 (works in 6.5.1) #12995 (both gr.update and gr.Slider variants)
• Test slider still works normally: dragging, number input, reset button
• Test visibility toggle: hidden → visible with different min/max/value

🤖 Generated with Claude Code

[hannahblair]

kumquat didnt work again

[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
🦄	Changes	detected!	Details

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Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/a688f99ca6f1f0a35d47e1537e39d406aaaf09e3/gradio-6.9.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@a688f99ca6f1f0a35d47e1537e39d406aaaf09e3#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/a688f99ca6f1f0a35d47e1537e39d406aaaf09e3/gradio-client-2.1.0.tgz

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/slider	patch
gradio	patch

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• Fix Slider property update freezing UI

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