Add support for scrollMargin option for intersection observers

[thebuilder]

Motivation

• Add support for a scrollMargin option to allow margins around nested scroll containers (and the root if it's a scroll container) to be considered by the observer.
• Propagate this option through the public types, hooks, component props, observer creation logic, test utilities, and Storybook so consumers can configure and visualize it.

Description

• Introduce IntersectionObserverInitWithOptions and extend public IntersectionOptions to include scrollMargin, trackVisibility, and delay where applicable.
• Wire scrollMargin into observe() and optionsToId() so observers are keyed and created correctly, and make observers recreate when scrollMargin changes in InView and hooks.
• Update the IntersectionObserver mock in test-utils.ts to expose scrollMargin so unit tests can assert the option is passed.
• Update README and Storybook stories/argTypes to document and showcase the scrollMargin option.

Fixes #749

[vercel]

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Project	Deployment	Actions	Updated (UTC)
react-intersection-observer	Ready	Preview, Comment	Jul 9, 2026 7:28am

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commit: a69589e