fix(ios): avoid unavailable libc++ exception_ptr symbol on iOS < 18

[vnahornyi]

Summary

• Replace std::make_exception_ptr with throw/catch and std::current_exception() in iOS/shared C++ exception paths, avoiding the missing libc++ symbol on iOS versions below 18 when built with Xcode 27.
• Add runtime coverage for destroying pending Promise<void> and Promise<double> instances.
• Assert that the error message survives the Swift/Kotlin/C++ callback boundary.

Closes #1652

Validation

• bun run typecheck in apps/example — passed.
• bun run test -- --watchman=false in packages/react-native-nitro-test — passed; the suite currently has one todo test.
• The built Nitrogen CLI regenerated bindings for react-native-nitro-test-external and react-native-nitro-test. The bun specs wrapper could not resolve nitrogen from PATH.
• The runtime harness could not run locally: the Android runner exited with AbortError before suites; iOS Simulator was unavailable.

[vercel]

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1 Skipped Deployment

Project	Deployment	Actions	Updated
nitro-docs	Skipped		Oct 7, 2026 7:14am UTC