### 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
}
    /**
     * If profiling was enabled, this returns an object containing the profile results from
     * each shard.  If profiling was not enabled, this will return null
     *
     * @return The profile results or an empty map
     */
    @Nullable
    public Map<String, SearchProfileShardResult> getProfileResults() {
        return internalResponse.profile();
    }
    /**
     * Returns info about what clusters the search was executed against. Available only in responses obtained
     * from a Cross Cluster Search request, otherwise <code>null</code>
     * @see Clusters
     */
    public Clusters getClusters() {
        return clusters;
    }
    @Override
    public Iterator<? extends ToXContent> toXContentChunked(ToXContent.Params params) {
        return Iterators.concat(
            ChunkedToXContentHelper.startObject(),
            this.innerToXContentChunked(params),
            ChunkedToXContentHelper.endObject()
        );
    }
    public Iterator<? extends ToXContent> innerToXContentChunked(ToXContent.Params params) {
        return Iterators.concat(
            ChunkedToXContentHelper.singleChunk(SearchResponse.this::headerToXContent),