### 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
);
                localSearchConsumer.accept(ccsLocalSearchRequest, ccsListener);
            }
        }
    }
    static SearchResponseMerger createSearchResponseMerger(
        SearchSourceBuilder source,
        SearchTimeProvider timeProvider,
        AggregationReduceContext.Builder aggReduceContextBuilder
    ) {
        final int from;
        final int size;
        final int trackTotalHitsUpTo;
        if (source == null) {
            from = SearchService.DEFAULT_FROM;
            size = SearchService.DEFAULT_SIZE;
            trackTotalHitsUpTo = SearchContext.DEFAULT_TRACK_TOTAL_HITS_UP_TO;
        } else {
            from = source.from() == -1 ? SearchService.DEFAULT_FROM : source.from();
            size = source.size() == -1 ? SearchService.DEFAULT_SIZE : source.size();
            trackTotalHitsUpTo = source.trackTotalHitsUpTo() == null
                ? SearchContext.DEFAULT_TRACK_TOTAL_HITS_UP_TO
                : source.trackTotalHitsUpTo();
            
            source.from(0);
            source.size(from + size);
        }
        return new SearchResponseMerger(from, size, trackTotalHitsUpTo, timeProvider, aggReduceContextBuilder);
    }
    /**