### 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
rewritten.pointInTimeBuilder().getKeepAlive(),
                                    remoteClusterIndices
                                );
                            } else {
                                remoteAliasFilters = new HashMap<>();
                                for (SearchShardsResponse searchShardsResponse : searchShardsResponses.values()) {
                                    remoteAliasFilters.putAll(searchShardsResponse.getAliasFilters());
                                }
                                remoteShardIterators = getRemoteShardsIterator(
                                    searchShardsResponses,
                                    remoteClusterIndices,
                                    remoteAliasFilters
                                );
                            }
                            executeSearch(
                                task,
                                timeProvider,
                                rewritten,
                                localIndices,
                                remoteShardIterators,
                                clusterNodeLookup,
                                clusterState,
                                remoteAliasFilters,
                                clusters,
                                searchContext,
                                searchPhaseProvider.apply(finalDelegate)
                            );
                        })
                    );
                }