### 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
* Has the search operation terminated early due to reaching
     * <code>terminateAfter</code>
     */
    public Boolean isTerminatedEarly() {
        return internalResponse.terminatedEarly();
    }
    /**
     * Returns the number of reduce phases applied to obtain this search response
     */
    public int getNumReducePhases() {
        return internalResponse.getNumReducePhases();
    }
    /**
     * How long the search took.
     */
    public TimeValue getTook() {
        return new TimeValue(tookInMillis);
    }
    /**
     * The total number of shards the search was executed on.
     */
    public int getTotalShards() {
        return totalShards;
    }
    /**
     * The successful number of shards the search was executed on.
     */
    public int getSuccessfulShards() {
        return successfulShards;
    }