### Description

`SearchResponse.Clusters` currently uses a `HashMap<String, AtomicReference>` for storing Cluster objects. The AtomicReference CAS swaps are done in a do/while loop in most cases (e.g., in `CCSSingleCoordinatorSearchProgressListener`).

This can be replaced with a `ConcurrentHashMap` in conjunction with either `compute()` method or the `replace(key, assumed_previous_value, value)` method for atomically swapping in a new Cluster object with a CAS operation, assuring that the updates don't lose data from competing threads doing separate Cluster object updates.

See: https://github.com/elastic/elasticsearch/pull/98457/files#r1310467586 
server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java
import org.elasticsearch.common.util.Maps;
import org.elasticsearch.common.util.concurrent.CountDown;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.index.Index;
import org.elasticsearch.index.IndexNotFoundException;
import org.elasticsearch.index.query.QueryBuilder;
import org.elasticsearch.index.query.Rewriteable;
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.index.shard.ShardNotFoundException;
import org.elasticsearch.indices.ExecutorSelector;
import org.elasticsearch.indices.breaker.CircuitBreakerService;
import org.elasticsearch.search.SearchService;
import org.elasticsearch.search.aggregations.AggregationReduceContext;
import org.elasticsearch.search.aggregations.InternalAggregations;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.search.internal.AliasFilter;
import org.elasticsearch.search.internal.InternalSearchResponse;
import org.elasticsearch.search.internal.SearchContext;
import org.elasticsearch.search.profile.SearchProfileResults;
import org.elasticsearch.search.profile.SearchProfileShardResult;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.tasks.TaskId;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.RemoteClusterAware;
import org.elasticsearch.transport.RemoteClusterService;
import org.elasticsearch.transport.RemoteTransportException;
import org.elasticsearch.transport.Transport;
import org.elasticsearch.transport.TransportRequestOptions;
import org.elasticsearch.transport.TransportService;