### 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
} else {
                    SearchResponse.Clusters clusters = new SearchResponse.Clusters(
                        localIndices,
                        remoteClusterIndices,
                        false,
                        alias -> remoteClusterService.isSkipUnavailable(alias)
                    );
                    
                    collectSearchShards(
                        rewritten.indicesOptions(),
                        rewritten.preference(),
                        rewritten.routing(),
                        rewritten.source() != null ? rewritten.source().query() : null,
                        Objects.requireNonNullElse(rewritten.allowPartialSearchResults(), searchService.defaultAllowPartialSearchResults()),
                        searchContext,
                        remoteClusterIndices,
                        clusters,
                        timeProvider,
                        transportService,
                        delegate.delegateFailureAndWrap((finalDelegate, searchShardsResponses) -> {
                            final BiFunction<String, String, DiscoveryNode> clusterNodeLookup = getRemoteClusterNodeLookup(
                                searchShardsResponses
                            );
                            final Map<String, AliasFilter> remoteAliasFilters;
                            final List<SearchShardIterator> remoteShardIterators;
                            if (searchContext != null) {
                                remoteAliasFilters = searchContext.aliasFilter();
                                remoteShardIterators = getRemoteShardsIteratorFromPointInTime(
                                    searchShardsResponses,
                                    searchContext,