fix(provider-limrun): preserve Unicode in Limrun iOS fill
Summary
On a Limrun iOS simulator, filling a field with Chinese or other non-ASCII text reports success while the field stays unchanged. ASCII entered the same way appears in the field. A direct value write of the same Chinese text is stored and read back by the app. Fill focused the field, selected its contents with Command-A, and then sent the string as hardware key events. Characters with no key code never become a key event, so they are dropped while the call still succeeds. An empty fill sent Delete instead of writing an empty value.
After text-entry focus arrives, fill writes the whole string with one setElementValue call, including an empty string and characters that have no hardware key. A supplied delay remains on the signature and the replacement stays a single write. type still sends key events, with per-character timing when a delay is set. The Limrun iOS docs and the text-entry tests follow that path, including no write when focus never arrives and failure when the value write is rejected.
Fixes #3819
Test plan
npx --no-install vitest run src/ios-interactor-text-entry.test.ts completed with 9 passed tests in 1 file.
Ran pnpm run test-app:install in a Linux container (localhost/osc-linux-node:22) for the agent-device LimrunIosInteractor change; it passed.