OptionalfetchMilliseconds a fetch may run before every caller waiting on it rejects with
CACHE_FETCH_TIMEOUT. The fetch is not cancelled; if it resolves later, its
value is still stored. Omit to wait indefinitely.
OptionalkvKV store override; defaults to the store passed to initialize
OptionalttlTime-to-live in seconds; omit or set <= 0 to cache without expiry
Options for cached and invalidate.