fix: isolate modal provider layout state

[huytdps13400]

Motivation

Multiple BottomSheetModalProvider instances currently pass the same module-level INITIAL_CONTAINER_LAYOUT object into useSharedValue. Since hosting-container updates mutate that object through .modify(), a nested provider can overwrite the root provider's height and offset, causing later root sheets to dismiss toward the nested container's shorter boundary.

This change gives each provider a fresh layout object and a separately cloned mutable offset. It preserves the existing values and shared-value API while preventing layout measurements from leaking across providers.

Fixes #2729.

Verification

• Confirmed immediately before pushing that no other open PR references [Bug]: BottomSheetModalProvider instances share one layout-state object — sheets dismiss short of the screen bottom after a nested provider re-measures #2729.
• TDD AST probe failed on master because useSharedValue received the module singleton directly, then passed after the outer object and nested offset were cloned.
• yarn typescript passed.
• yarn build passed for CommonJS, ESM, and TypeScript declarations; both JavaScript outputs contain the nested clone.
• yarn biome check --error-on-warnings src/components/bottomSheetModalProvider/BottomSheetModalProvider.tsx passed.
• The repository pre-commit Biome checks and commitlint passed.
• Full yarn lint remains blocked by the existing optional-chain warning in src/hooks/useBoundingClientRect.ts:54, outside this diff.

The repository currently has no unit-test files or test script, so no persistent Jest suite was available. I did not run the nested iOS page-sheet reproduction on a device; runtime UI verification remains outstanding.

[github-actions]

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