### 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
: new SearchProfileResults(profileResults);
                    InternalSearchResponse internalSearchResponse = new InternalSearchResponse(
                        searchResponse.getHits(),
                        (InternalAggregations) searchResponse.getAggregations(),
                        searchResponse.getSuggest(),
                        profile,
                        searchResponse.isTimedOut(),
                        searchResponse.isTerminatedEarly(),
                        searchResponse.getNumReducePhases()
                    );
                    listener.onResponse(
                        new SearchResponse(
                            internalSearchResponse,
                            searchResponse.getScrollId(),
                            searchResponse.getTotalShards(),
                            searchResponse.getSuccessfulShards(),
                            searchResponse.getSkippedShards(),
                            timeProvider.buildTookInMillis(),
                            searchResponse.getShardFailures(),
                            clusters,
                            searchResponse.pointInTimeId()
                        )
                    );
                }
                @Override
                public void onFailure(Exception e) {
                    ShardSearchFailure failure = new ShardSearchFailure(e);
                    logCCSError(failure, clusterAlias, skipUnavailable);
                    ccsClusterInfoUpdate(failure, clusters.getCluster(clusterAlias), skipUnavailable);
                    if (skipUnavailable) {