Fix opt-in flag typing and bootstrap loading state

[roncohen]

Summary

• narrow React and Vue OptInFlag.key to each SDK's generated FlagKey, so values returned by useOptInFlags() pass directly to useSetOptIn()
• expose browser opt-in loading through getIsLoadingOptInFlags() and the optInFlagsLoadingUpdated event
• return { flags, isLoading } from the React and Vue useOptInFlags() APIs
• report opt-in isLoading only while bootstrapped providers fetch opt-in metadata on first use; regular providers continue to use useIsLoading() for their normal initial flags request
• support provider-level and per-hook Suspense in React while regular flags or required bootstrapped opt-in metadata load
• keep loading tied to the latest context/bootstrap generation so stale or concurrent refreshes cannot clear newer loading state
• document manual spinner/empty-state handling, the bootstrapping-specific loading case, and React Suspense behavior

API

React:

const { flags, isLoading } = useOptInFlags();

Vue (both values are computed refs and are automatically unwrapped in templates):

const { flags, isLoading } = useOptInFlags();

With a bootstrapped provider, isLoading is true while fetching opt-in metadata on first use. With a regular provider, opt-in metadata arrives with the normal flags response and useIsLoading() covers that initial request.

Unaugmented SDK consumers still get string flag keys; generated/augmented consumers get their existing FlagKey union without weakening other typed flag APIs.

Tests

Added coverage for:

• generated React and Vue Flags type augmentation and direct flag.key usage with useSetOptIn()
• regular-provider loading versus bootstrapped opt-in metadata loading
• successful and failed bootstrapped metadata refreshes
• context races, newly applied bootstrap state, stale refreshes, and offline mode
• React and Vue reactive rerenders
• React Suspense with regular providers and missing bootstrap metadata
• React Suspense failure recovery and per-hook opt-out

Commands run:

• yarn workspace @reflag/browser-sdk test
• yarn workspace @reflag/react-sdk test
• yarn workspace @reflag/react-sdk test:types
• yarn workspace @reflag/vue-sdk test
• yarn workspace @reflag/vue-sdk test:types
• yarn lint
• yarn fmt
• yarn workspace @reflag/browser-sdk build
• yarn workspace @reflag/react-sdk build
• yarn workspace @reflag/react-native-sdk build
• yarn workspace @reflag/vue-sdk build
• yarn changeset status