### 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/internalClusterTest/java/org/elasticsearch/action/search/CCSPointInTimeIT.java
}
    }
    private static void assertOneSuccessfulShard(SearchResponse.Cluster cluster) {
        assertThat(cluster.getTotalShards(), equalTo(1));
        assertThat(cluster.getSuccessfulShards(), equalTo(1));
        assertThat(cluster.getFailedShards(), equalTo(0));
        assertThat(cluster.getFailures().size(), equalTo(0));
        assertThat(cluster.getStatus(), equalTo(SearchResponse.Cluster.Status.SUCCESSFUL));
        assertThat(cluster.getTook().millis(), greaterThanOrEqualTo(0L));
        assertFalse(cluster.isTimedOut());
    }
    private static void assertOneFailedShard(SearchResponse.Cluster cluster, int totalShards) {
        assertThat(cluster.getSuccessfulShards(), equalTo(totalShards - 1));
        assertThat(cluster.getFailedShards(), equalTo(1));
        assertThat(cluster.getFailures().size(), equalTo(1));
        assertThat(cluster.getFailures().get(0).reason(), containsString("index corrupted"));
        assertThat(cluster.getStatus(), equalTo(SearchResponse.Cluster.Status.PARTIAL));
        assertThat(cluster.getTook().millis(), greaterThanOrEqualTo(0L));
        assertFalse(cluster.isTimedOut());
    }
    private String openPointInTime(String[] indices, TimeValue keepAlive) {
        OpenPointInTimeRequest request = new OpenPointInTimeRequest(indices).keepAlive(keepAlive);
        final OpenPointInTimeResponse response = client().execute(OpenPointInTimeAction.INSTANCE, request).actionGet();
        return response.getPointInTimeId();
    }
    private void closePointInTime(String readerId) {
        client().execute(ClosePointInTimeAction.INSTANCE, new ClosePointInTimeRequest(readerId)).actionGet();
    }
}