Wrapping split and merge in a CollectionRouter::route() function prevents StaleConfig errors from being exposed to the user.

CollectionRouter::route() is essentially a wrapper that retries the operation and refreshes router metadata when a shard returns StaleConfig, indicating that the shard version used for routing was outdated.

This retry logic was previously handled by the mongos service entry point, but it was removed recently and was never added to the split and merge commands.