Just like the Shard class make use of runWithRetryStrategy to properly retry with a backoff, KeysCollectionClientDirect should also consider using a retry strategy instead of implementing its own loop.

The predicate isRetriableError should also be updated to handle kStrictlyNotIdempotent. Using a switch case without a default and a unreachable statement at the end should enable warnings and clang-tidy to warn us of added enumerators instead of triggering the invariant.

See SPM-4003 for more detail on retryability.