Fix useColorScheme subscription lifecycle

[huytdps13400]

Summary

• keep each useColorScheme Appearance subscription active for the hook lifetime
• avoid removing and re-adding listeners after unrelated component rerenders
• add regression coverage for rerender and unmount subscription behavior

Fixes #2848.

Verification

• focused useColorScheme Jest test: RED before the fix (2 registrations after rerender), GREEN after the fix
• npm run test: Flow, Prettier, ESLint, 47 DOM suites / 713 tests passed, 3 Node suites / 6 tests passed
• npm run build -w react-native-web: Flow, ESM, and CommonJS builds passed
• Chromium runtime: two hook instances retained 2 active listeners with 0 removals after rerender; a simulated prefers-color-scheme flip updated both values from light to dark; console remained clean
• git diff --check: passed

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