### 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(shardFailures.length, greaterThan(0));
        String json = Strings.toString(
            ChunkedToXContent.wrapAsToXContent(searchResponseAfterCompletion)
                .toXContent(XContentFactory.jsonBuilder(), ToXContent.EMPTY_PARAMS)
        );
        assertThat(json, matchesRegex(".*task (was)?\s*cancelled.*"));
    }
    public void testCancelViaAsyncSearchDelete() throws Exception {
        Map<String, Object> testClusterInfo = setupTwoClusters();
        String localIndex = (String) testClusterInfo.get("local.index");
        String remoteIndex = (String) testClusterInfo.get("remote.index");
        SearchListenerPlugin.blockQueryPhase();
        SubmitAsyncSearchRequest request = new SubmitAsyncSearchRequest(localIndex, REMOTE_CLUSTER + ":" + remoteIndex);
        request.setCcsMinimizeRoundtrips(randomBoolean());
        request.setWaitForCompletionTimeout(TimeValue.timeValueMillis(1));
        request.setKeepOnCompletion(true);
        if (randomBoolean()) {
            request.setBatchedReduceSize(randomIntBetween(2, 256));
        }
        request.getSearchRequest().allowPartialSearchResults(false);
        request.getSearchRequest().source(new SearchSourceBuilder().query(new MatchAllQueryBuilder()).size(10));
        AsyncSearchResponse response = submitAsyncSearch(request);
        assertNotNull(response.getSearchResponse());
        assertTrue(response.isRunning());
        SearchListenerPlugin.waitSearchStarted();
        try {
            ListTasksResponse listTasksResponse = client(LOCAL_CLUSTER).admin()
                .cluster()
                .prepareListTasks()
                .setActions(SearchAction.INSTANCE.name())