### 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/search/ccs/CrossClusterSearchIT.java
ThrowingQueryBuilder queryBuilder = new ThrowingQueryBuilder(randomLong(), new IllegalStateException("index corrupted"), 0);
        searchRequest.source(new SearchSourceBuilder().query(queryBuilder).size(10));
        SearchResponse searchResponse = client(LOCAL_CLUSTER).search(searchRequest).get();
        assertNotNull(searchResponse);
        SearchResponse.Clusters clusters = searchResponse.getClusters();
        assertThat(clusters.getTotal(), equalTo(1));
        assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.SUCCESSFUL), equalTo(0));
        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(1));
        assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.FAILED), equalTo(0));
        assertNull(clusters.getCluster(RemoteClusterAware.LOCAL_CLUSTER_GROUP_KEY));
        SearchResponse.Cluster remoteClusterSearchInfo = clusters.getCluster(REMOTE_CLUSTER).get();
        assertNotNull(remoteClusterSearchInfo);
        assertOneFailedShard(remoteClusterSearchInfo, remoteNumShards);
    }
    public void testRemoteClusterOnlyCCSWithFailuresOnAllShards() throws Exception {
        Map<String, Object> testClusterInfo = setupTwoClusters();
        String remoteIndex = (String) testClusterInfo.get("remote.index");
        boolean skipUnavailable = (Boolean) testClusterInfo.get("remote.skip_unavailable");
        PlainActionFuture<SearchResponse> queryFuture = new PlainActionFuture<>();
        SearchRequest searchRequest = new SearchRequest(REMOTE_CLUSTER + ":" + remoteIndex);
        searchRequest.allowPartialSearchResults(true);
        searchRequest.setCcsMinimizeRoundtrips(randomBoolean());
        if (randomBoolean()) {
            searchRequest.setBatchedReduceSize(randomIntBetween(3, 20));
        }
        if (randomBoolean()) {
            searchRequest.searchType(SearchType.DFS_QUERY_THEN_FETCH);