Skill: Add TypeScript API Tests

Behavior changes under src/ should be covered by the Jest suites at packages/react-native-executorch/__tests__/. They run on a laptop or a CI runner — no simulator, no device, no .pte — and finish in a few seconds. Reuse existing coverage for comments or changes with no observable behavior; do not add tests that merely restate the implementation. Fake-runtime tests exercise TypeScript logic, not production C++ or actual delegated model inference.

yarn workspace react-native-executorch test
yarn workspace react-native-executorch test __tests__/tasks   # one directory
yarn workspace react-native-executorch test -u                # update snapshots

From the repository root, yarn workspace react-native-executorch typecheck includes __tests__/. Root yarn typecheck also builds and checks other workspaces; see the verification matrix.