### 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
.setActions(SearchAction.INSTANCE.name())
                .get();
            List<TaskInfo> remoteTasks = remoteTasksResponse.getTasks();
            assertThat(remoteTasks.size(), equalTo(0));
        });
        assertBusy(() -> {
            final Iterable<TransportService> transportServices = cluster(REMOTE_CLUSTER).getInstances(TransportService.class);
            for (TransportService transportService : transportServices) {
                assertThat(transportService.getTaskManager().getBannedTaskIds(), Matchers.empty());
            }
        });
    }
    private static void assertAllShardsFailed(boolean minimizeRoundtrips, SearchResponse.Cluster cluster, int numShards) {
        if (minimizeRoundtrips) {
            assertNull(cluster.getTotalShards());
            assertNull(cluster.getSuccessfulShards());
            assertNull(cluster.getSkippedShards());
            assertNull(cluster.getFailedShards());
            assertThat(cluster.getFailures().size(), equalTo(1));
        } else {
            assertThat(cluster.getTotalShards(), equalTo(numShards));
            assertThat(cluster.getSuccessfulShards(), equalTo(0));
            assertThat(cluster.getSkippedShards(), equalTo(0));
            assertThat(cluster.getFailedShards(), equalTo(numShards));
            assertThat(cluster.getFailures().size(), equalTo(numShards));
        }
        assertNull(cluster.getTook());
        assertFalse(cluster.isTimedOut());
        ShardSearchFailure shardSearchFailure = cluster.getFailures().get(0);
        assertTrue("should have 'index corrupted' in reason", shardSearchFailure.reason().contains("index corrupted"));