Quorum read consistency decision

A Dynamo-style store uses N replicas with read quorum R and write quorum W. A read collects responses from some replicas, each a pair [version, value] where higher integer version is fresher. The read succeeds only if at least R replicas responded. Given N, R, W, and the list of responses, return a 3-element list [ok, value, repair_count]: ok is True iff strong consistency is guaranteed for this read (R + W > N) AND at least R replicas responded; value is the value attached to the highest version among responders (empty string if no responses); repair_count is the number of responding replicas whose version is strictly less than the max version (these are stale and need read-repair).