fix: observe fallbackInView option updates in InView

[feritcemkahraman]

When IntersectionObserver is unavailable, changing <InView fallbackInView> from true to false leaves the rendered visibility and callback at the old value. The class component's observer-option comparison does not include this prop.

Include fallbackInView alongside the other observer options. The browser regression rerenders the same component and verifies both rendered state and onChange. It fails before the fix.

Validation:

• All 99 tests in 7 files pass (real Chromium browser project plus Node SSR project). A temporary local config points Playwright to the installed Chromium; committed config unchanged.
• TypeScript noEmit passes.
• Package-wide Biome lint and changed-file Biome check pass. Full formatting check reports existing Windows checkout CRLF differences in other files; those are not included in this fix.
• tsup builds CJS, ESM, declarations, and test-utils; the existing dist/esm compatibility copy was reproduced with native Windows commands.
• All four size-limit checks pass: InView 1.37 kB, useInView 1.35 kB, useOnInView 1.11 kB, observe 778 B.
• git diff --check passes.

The Storybook/docs app builds and packed compatibility matrix were not run for this class-component option fix.

Additional validation completed after opening: publint reports no errors (only an engines.node suggestion), and the packed @arethetypeswrong/cli --pack check reports no problems for both exports across node10, node16 CJS/ESM, and bundler modes.

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Project	Deployment	Actions	Updated
react-intersection-observer	Ready	Preview	Oct 10, 2026 6:10pm UTC

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