### 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 (clusterAlias.equals("")) {
                name = "(local)";
            }
            builder.startObject(name);
            {
                builder.field(STATUS_FIELD.getPreferredName(), getStatus().toString());
                builder.field(INDICES_FIELD.getPreferredName(), indexExpression);
                if (took != null) {
                    builder.field(TOOK.getPreferredName(), took.millis());
                }
                builder.field(TIMED_OUT.getPreferredName(), timedOut);
                if (totalShards != null) {
                    builder.startObject(RestActions._SHARDS_FIELD.getPreferredName());
                    builder.field(RestActions.TOTAL_FIELD.getPreferredName(), totalShards);
                    if (successfulShards != null) {
                        builder.field(RestActions.SUCCESSFUL_FIELD.getPreferredName(), successfulShards);
                    }
                    if (skippedShards != null) {
                        builder.field(RestActions.SKIPPED_FIELD.getPreferredName(), skippedShards);
                    }
                    if (failedShards != null) {
                        builder.field(RestActions.FAILED_FIELD.getPreferredName(), failedShards);
                    }
                    builder.endObject();
                }
                if (failures != null && failures.size() > 0) {
                    builder.startArray(RestActions.FAILURES_FIELD.getPreferredName());
                    for (ShardSearchFailure failure : failures) {
                        failure.toXContent(builder, params);
                    }