### 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
if (skipUnavailable) {
                assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.SKIPPED), equalTo(1));
                assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.FAILED), equalTo(0));
            } else {
                assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.SKIPPED), equalTo(0));
                assertThat(clusters.getClusterStateCount(SearchResponse.Cluster.Status.FAILED), equalTo(1));
            }
            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();
            assertNotNull(remoteClusterSearchInfo);
            SearchResponse.Cluster.Status expectedStatus = skipUnavailable
                ? SearchResponse.Cluster.Status.SKIPPED
                : SearchResponse.Cluster.Status.FAILED;
            assertThat(remoteClusterSearchInfo.getStatus(), equalTo(expectedStatus));
            if (clusters.isCcsMinimizeRoundtrips()) {
                assertNull(remoteClusterSearchInfo.getTotalShards());
                assertNull(remoteClusterSearchInfo.getSuccessfulShards());
                assertNull(remoteClusterSearchInfo.getSkippedShards());
                assertNull(remoteClusterSearchInfo.getFailedShards());
                assertThat(remoteClusterSearchInfo.getFailures().size(), equalTo(1));
            } else {
                assertThat(remoteClusterSearchInfo.getTotalShards(), equalTo(remoteNumShards));