### 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
assertThat(remoteClusterSearchInfo.getSuccessfulShards(), equalTo(0));
                assertThat(remoteClusterSearchInfo.getSkippedShards(), equalTo(0));
                assertThat(remoteClusterSearchInfo.getFailedShards(), equalTo(remoteNumShards));
                assertThat(remoteClusterSearchInfo.getFailures().size(), equalTo(remoteNumShards));
            }
            assertNull(remoteClusterSearchInfo.getTook());
            assertFalse(remoteClusterSearchInfo.isTimedOut());
            ShardSearchFailure remoteShardSearchFailure = remoteClusterSearchInfo.getFailures().get(0);
            assertTrue("should have 'index corrupted' in reason", remoteShardSearchFailure.reason().contains("index corrupted"));
        }
    }
    public void testCCSWithSearchTimeoutOnRemoteCluster() throws Exception {
        Map<String, Object> testClusterInfo = setupTwoClusters();
        String localIndex = (String) testClusterInfo.get("local.index");
        String remoteIndex = (String) testClusterInfo.get("remote.index");
        int localNumShards = (Integer) testClusterInfo.get("local.num_shards");
        int remoteNumShards = (Integer) testClusterInfo.get("remote.num_shards");
        SearchRequest searchRequest = new SearchRequest(localIndex, 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);
        }
        if (randomBoolean()) {
            searchRequest.setPreFilterShardSize(1);
        }
        TimeValue searchTimeout = new TimeValue(100, TimeUnit.MILLISECONDS);