### 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
List<TaskInfo> tasks = listTasksResponse.getTasks();
            assertThat(tasks.size(), equalTo(0));
            ListTasksResponse remoteTasksResponse = client(REMOTE_CLUSTER).admin()
                .cluster()
                .prepareListTasks()
                .setActions(SearchAction.INSTANCE.name())
                .get();
            List<TaskInfo> remoteTasks = remoteTasksResponse.getTasks();
            assertThat(remoteTasks.size(), equalTo(0));
        });
        AsyncStatusResponse statusResponse = getAsyncStatus(response.getId());
        assertFalse(statusResponse.isRunning());
        assertTrue(statusResponse.isPartial());
        assertEquals(0, statusResponse.getSuccessfulShards());
        assertEquals(0, statusResponse.getSkippedShards());
        assertThat(statusResponse.getFailedShards(), greaterThanOrEqualTo(1));
        waitForSearchTasksToFinish();
    }
    private void waitForSearchTasksToFinish() throws Exception {
        assertBusy(() -> {
            ListTasksResponse listTasksResponse = client(LOCAL_CLUSTER).admin()
                .cluster()
                .prepareListTasks()
                .setActions(SearchAction.INSTANCE.name())
                .get();
            List<TaskInfo> tasks = listTasksResponse.getTasks();
            assertThat(tasks.size(), equalTo(0));
            ListTasksResponse remoteTasksResponse = client(REMOTE_CLUSTER).admin()
                .cluster()
                .prepareListTasks()