### 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/SearchResponse.java
int size = in.readVInt();
        if (size == 0) {
            shardFailures = ShardSearchFailure.EMPTY_ARRAY;
        } else {
            shardFailures = new ShardSearchFailure[size];
            for (int i = 0; i < shardFailures.length; i++) {
                shardFailures[i] = readShardSearchFailure(in);
            }
        }
        clusters = new Clusters(in);
        scrollId = in.readOptionalString();
        tookInMillis = in.readVLong();
        skippedShards = in.readVInt();
        if (in.getTransportVersion().onOrAfter(TransportVersions.V_7_10_0)) {
            pointInTimeId = in.readOptionalString();
        } else {
            pointInTimeId = null;
        }
    }
    public SearchResponse(
        SearchResponseSections internalResponse,
        String scrollId,
        int totalShards,
        int successfulShards,
        int skippedShards,
        long tookInMillis,
        ShardSearchFailure[] shardFailures,
        Clusters clusters
    ) {
        this(internalResponse, scrollId, totalShards, successfulShards, skippedShards, tookInMillis, shardFailures, clusters, null);