fix: support callback forwarded refs

[wanxiankai]

Description

Fixes #805.

useEnsuredForwardedRef previously treated every forwarded ref as a mutable ref object. Callback refs passed through ensuredForwardRef therefore received a .current property assignment instead of being invoked. This updates the helper to accept React ForwardedRef<T>, assign object refs and callback refs correctly, and call callback refs with null on cleanup.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as before)

Checklist

• Read the Contributing Guide
• Perform a code self-review
• Comment the code, particularly in hard-to-understand areas
• Add documentation
• Add hook's story at Storybook
• Cover changes with tests
• Ensure the test suite passes (yarn test)
• Provide 100% tests coverage
• Make sure code lints (yarn lint). Fix it with yarn lint:fix in case of failure.
• Make sure types are fine (yarn lint:types).

Verification

• yarn test tests/useEnsuredForwardedRef.test.tsx --watchman=false
• yarn test --watchman=false
• yarn lint:types
• ./node_modules/.bin/eslint src/useEnsuredForwardedRef.ts tests/useEnsuredForwardedRef.test.tsx
• yarn lint (passes with existing warnings)
• yarn build