[fix] Clipboard: align setString return type with React Native

[KuroGeo]

Align Clipboard.setString with React Native's void return contract, following the review feedback. React Native's NativeClipboard spec does not return a copy-success status.

Remove the Web-specific boolean return and update the API documentation and clipboard example accordingly. This changes the previous Web return contract: callers should no longer use the result as a copy-success indication. The extra tests from the initial revision have been removed as requested; copying, exception handling, and cleanup remain unchanged.

Validation on Node 24.13.0:

• Complete existing DOM / Node suites: 721 tests passed, 6 existing skips, 220 snapshots passed.
• Repository formatting, lint, and diff checks pass.
• Isolated local checks confirm the method returns no value and cleans up its temporary node and selection whether the browser command succeeds, returns false, or throws.
• Flow is not verified locally: the pinned 0.148.0 macOS binary exits with architecture error -86 on this arm64 host. Upstream CI runs the checker on Linux.

AI assistance: OpenAI Codex implemented the initial fix and this revision on behalf of @KuroGeo.

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[zoontek]

@KuroGeo Clipboard should return void (see https://github.com/react/react-native/blob/v0.88.0-rc.4/packages/react-native/src/private/specs_DEPRECATED/modules/NativeClipboard.js#L18). Also, there's no need for extra tests.

[KuroGeo]

Updated in 891bfc6. Clipboard.setString now returns void, and the API docs and clipboard example have been updated to match. The additional tests from the initial revision have been removed.

The existing DOM and Node suites pass: 721 tests passed, 6 existing skips, and 220 snapshots passed. Formatting and lint checks also pass.

[zoontek]

Closing this. The divergence from react-native is explained in the docs, and Clipboard is deprecated for a while and will be removed in React Native 0.89. It does not worth it to introduce a breaking change for such a short amount of time (as it will be removed from here too)