This change adds a fast path for extracting the cluster time from a change stream resume token.
The fast path only extracts and validates the first 18 bytes of the hex resume token string, which contain the timestamp part. It does not decode nor validate all remaining bytes. This can save substantial work, as change stream resume tokens can be of arbitrary length, and converting the full string to a proper `ResumeToken` only to extract the cluster time part has substantial costs.