int requestsToSend() {
        return requestsToSend.size();
    }
Group partitions by leader. Topic partitions from `timestampsToSearch` for which
the leader is not known are kept as `remainingToSearch` in the `listOffsetsRequestState`

@param timestampsToSearch      The mapping from partitions to the target timestamps
@param listOffsetsRequestState Optional request state that will be extended by adding to its
                               `remainingToSearch` map all partitions for which the
                               request cannot be performed due to unknown leader (need
                               metadata update).
clients/src/main/java/org/apache/kafka/clients/consumer/internals/OffsetsRequestManager.java