Fix iOS Metro reload after initial bundle failure

[janicduplessis]

Summary:

If the first bundle request fails on bridgeless iOS, Metro reload does nothing — the app sits on the error screen and has to be killed and relaunched, even once the source is fixed. Android already handles this.

The cause is timing. RCTInstance resolves the DevSettings TurboModule only inside _loadJSBundle's success callback, and RCTDevSettings.initialize is what registers the Metro reload message handler. No successful first load means no handler, so the app never becomes a Metro reload peer.

This resolves DevSettings at the top of _loadJSBundle, before the request is issued, so the handler is registered regardless of how that request turns out. The callback keeps its own resolution for the HMR setup that follows it.

Changelog:

[IOS] [FIXED] - Allow Metro reload after an initial bundle-load failure.

Test Plan:

On RNTester (iOS 26.5 simulator), launched with an unresolved import so the initial bundle fails, then restored the source and waited 10 seconds: the error stayed and Metro received no bundle request, confirming the app was not a reload peer. Sending {version: 2, method: "reload"} to Metro then made it request a corrected bundle and recover in place, native PID 95823 unchanged. A second consecutive reload also worked.

Same scenario on Android RNTester as the reference: it already receives the Metro command on the initial-error path, recovering with PID 14848 unchanged.

[meta-codesync]

@javache has imported this pull request. If you are a Meta employee, you can view this in D119072108.