### 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/main/java/org/elasticsearch/action/search/SearchResponse.java
if (RestActions.FAILURES_FIELD.match(currentFieldName, parser.getDeprecationHandler())) {
                        while ((token = parser.nextToken()) != Token.END_ARRAY) {
                            failures.add(ShardSearchFailure.fromXContent(parser));
                        }
                    } else {
                        parser.skipChildren();
                    }
                } else {
                    parser.skipChildren();
                }
            }
            Integer totalShardsFinal = totalShards == -1 ? null : totalShards;
            Integer successfulShardsFinal = successfulShards == -1 ? null : successfulShards;
            Integer skippedShardsFinal = skippedShards == -1 ? null : skippedShards;
            Integer failedShardsFinal = failedShards == -1 ? null : failedShards;
            TimeValue tookTimeValue = took == -1L ? null : new TimeValue(took);
            boolean skipUnavailable = SKIP_UNAVAILABLE_DEFAULT;  
            return new Cluster(
                clusterName,
                indexExpression,
                skipUnavailable,
                SearchResponse.Cluster.Status.valueOf(status.toUpperCase(Locale.ROOT)),
                totalShardsFinal,
                successfulShardsFinal,
                skippedShardsFinal,
                failedShardsFinal,
                failures,
                tookTimeValue,
                timedOut
            );