Repaired data tracking on a read coordinator is susceptible to races between local and remote requests

At read time on a coordinator which is also a replica, the local and remote reads can race such that the remote responses are received while the local read is executing. If the remote responses are mismatching, triggering a DigestMismatchException and subsequent round of full data reads and read repair, the local runnable may find the isTrackingRepairedStatus flag flipped mid-execution. If this happens after a certain point in execution, it would mean
that the RepairedDataInfo instance in use is the singleton null object RepairedDataInfo.NULL_REPAIRED_DATA_INFO. If this happens, it can lead to an NPE when calling RepairedDataInfo::extend when the local results are iterated.