### 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
}
    public SearchResponse(
        SearchResponseSections internalResponse,
        String scrollId,
        int totalShards,
        int successfulShards,
        int skippedShards,
        long tookInMillis,
        ShardSearchFailure[] shardFailures,
        Clusters clusters,
        String pointInTimeId
    ) {
        this.internalResponse = internalResponse;
        this.scrollId = scrollId;
        this.pointInTimeId = pointInTimeId;
        this.clusters = clusters;
        this.totalShards = totalShards;
        this.successfulShards = successfulShards;
        this.skippedShards = skippedShards;
        this.tookInMillis = tookInMillis;
        this.shardFailures = shardFailures;
        assert skippedShards <= totalShards : "skipped: " + skippedShards + " total: " + totalShards;
        assert scrollId == null || pointInTimeId == null
            : "SearchResponse can't have both scrollId [" + scrollId + "] and searchContextId [" + pointInTimeId + "]";
    }
    public RestStatus status() {
        return RestStatus.status(successfulShards, totalShards, shardFailures);
    }
    public SearchResponseSections getInternalResponse() {
        return internalResponse;