### 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/TransportSearchAction.java
current.addSuppressed(previous);
                        return current;
                    });
                }
            }
            maybeFinish();
        }
        private void maybeFinish() {
            if (countDown.countDown()) {
                Exception exception = exceptions.get();
                if (exception == null) {
                    FinalResponse response;
                    try {
                        response = createFinalResponse();
                    } catch (Exception e) {
                        originalListener.onFailure(e);
                        return;
                    }
                    originalListener.onResponse(response);
                } else {
                    originalListener.onFailure(exceptions.get());
                }
            }
        }
        abstract FinalResponse createFinalResponse();
    }
    /**
     * In order to gather data on what types of CCS errors happen in the field, we will log
     * them using the ShardSearchFailure XContent (JSON), which supplies information about underlying
     * causes of shard failures.