buildAnonymousContext function
Build a stable anonymous EvalContext. A UUID is minted on first use and
persisted through storage so the same install lands in the same targeting
bucket across restarts. When storage is an InMemoryStorage (the
default), the key is stable only for the process lifetime.
The resulting shape mirrors the other feat SDKs:
{ targetingKey: uuid, user: { key: uuid, anonymous: true } }.
Implementation
Future<EvalContext> buildAnonymousContext(FeatStorage storage) async {
final key = await _resolveOrMintKey(storage);
return EvalContext.user(key, anonymous: true);
}