### 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 
x-pack/plugin/async-search/src/internalClusterTest/java/org/elasticsearch/xpack/search/CrossClusterAsyncSearchIT.java
assertThat(remoteClusterSearchInfo.getStatus(), equalTo(SearchResponse.Cluster.Status.SUCCESSFUL));
            assertThat(remoteClusterSearchInfo.getTotalShards(), equalTo(remoteNumShards));
            assertThat(remoteClusterSearchInfo.getSuccessfulShards(), equalTo(remoteNumShards));
            assertThat(remoteClusterSearchInfo.getSkippedShards(), equalTo(0));
            assertThat(remoteClusterSearchInfo.getFailedShards(), equalTo(0));
            assertThat(remoteClusterSearchInfo.getFailures().size(), equalTo(0));
            assertThat(remoteClusterSearchInfo.getTook().millis(), greaterThan(0L));
        }
        
        {
            AsyncStatusResponse statusResponse = getAsyncStatus(response.getId());
            assertFalse(statusResponse.isPartial());
            SearchResponse.Clusters clusters = statusResponse.getClusters();
            assertFalse("search cluster results should NOT be marked as partial", clusters.hasPartialResults());
            assertThat(clusters.getTotal(), equalTo(2));
            assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.SUCCESSFUL), equalTo(2));
            assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.SKIPPED), equalTo(0));
            assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.RUNNING), equalTo(0));
            assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.PARTIAL), equalTo(0));
            assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.FAILED), equalTo(0));
            SearchResponse.Cluster localClusterSearchInfo = clusters.getCluster(RemoteClusterAware.LOCAL_CLUSTER_GROUP_KEY).get();
            assertNotNull(localClusterSearchInfo);
            assertThat(localClusterSearchInfo.getStatus(), equalTo(SearchResponse.Cluster.Status.SUCCESSFUL));
            assertThat(localClusterSearchInfo.getTotalShards(), equalTo(localNumShards));
            assertThat(localClusterSearchInfo.getSuccessfulShards(), equalTo(localNumShards));
            assertThat(localClusterSearchInfo.getSkippedShards(), equalTo(0));
            assertThat(localClusterSearchInfo.getFailedShards(), equalTo(0));
            assertThat(localClusterSearchInfo.getFailures().size(), equalTo(0));
            assertThat(localClusterSearchInfo.getTook().millis(), greaterThan(0L));
            SearchResponse.Cluster remoteClusterSearchInfo = clusters.getCluster(REMOTE_CLUSTER).get();