### 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
* Creates a new Cluster object using the {@link ShardSearchFailure} info and skip_unavailable
     * flag to set Status. The new Cluster object is swapped into the clusterRef {@link AtomicReference}.
     */
    static void ccsClusterInfoUpdate(
        ShardSearchFailure failure,
        AtomicReference<SearchResponse.Cluster> clusterRef,
        boolean skipUnavailable
    ) {
        SearchResponse.Cluster.Status status;
        if (skipUnavailable) {
            status = SearchResponse.Cluster.Status.SKIPPED;
        } else {
            status = SearchResponse.Cluster.Status.FAILED;
        }
        boolean swapped;
        do {
            SearchResponse.Cluster orig = clusterRef.get();
            
            List<ShardSearchFailure> failures = CollectionUtils.appendToCopy(orig.getFailures(), failure);
            SearchResponse.Cluster updated = new SearchResponse.Cluster.Builder(orig).setStatus(status).setFailures(failures).build();
            swapped = clusterRef.compareAndSet(orig, updated);
        } while (swapped == false);
    }
    /**
     * Helper method common to multiple ccs_minimize_roundtrips=true code paths.
     * Used to update a specific SearchResponse.Cluster object state based upon
     * the SearchResponse coming from the cluster coordinator the search was performed on.
     * @param searchResponse SearchResponse from cluster sub-search
     * @param clusterRef AtomicReference of the Cluster object to be updated
     */