fix: don't call onMessage callback twice when it throws

[RaphaelFakhri]

Summary

ReactNativeBrownfield.onMessage wraps both JSON.parse and the user callback in one try/catch. When the callback throws while it handles a valid JSON message, the catch branch calls the callback a second time, now with the raw message string as data. The original error is lost.

For example, with a native host that posts {"type":"login"}:

ReactNativeBrownfield.onMessage((event) => {
  handle((event.data as { type: string }).type); // throws inside handle()
});

The callback runs once with { type: 'login' }, then again with '{"type":"login"}'. The second call reads .type of a string and the original error from handle() never reaches the developer.

This change limits the try/catch to JSON.parse and calls the callback once, outside of it. Errors thrown by the callback now propagate as they do for any other event listener.

Test plan

• Added packages/react-native-brownfield/src/__tests__/onMessage.test.ts, which covers JSON payloads, non-JSON payloads, a throwing callback and remove().
• Without the fix, does not call the callback again when it throws fails because the callback is called twice. With the fix, all 4 tests pass.
• yarn test, yarn lint and yarn typecheck in packages/react-native-brownfield pass (13 files, 114 tests).
• Added a patch changeset for @callstack/react-native-brownfield.

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