### 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/test/java/org/elasticsearch/xpack/search/AsyncSearchResponseTests.java
"failed" : 0
                    },
                    "_clusters" : {
                      "total" : 3,
                      "successful" : 0,
                      "skipped" : 0,
                      "running" : 3,
                      "partial" : 0,
                      "failed" : 0,
                      "details" : {
                        "cluster_1" : {
                          "status" : "running",
                          "indices" : "foo,bar*",
                          "timed_out" : false
                        },
                        "cluster_2" : {
                          "status" : "running",
                          "indices" : "foo,bar*",
                          "timed_out" : false
                        },
                        "cluster_0" : {
                          "status" : "running",
                          "indices" : "foo,bar*",
                          "timed_out" : false
                        }
                      }
                    },
                    "hits" : {
                      "max_score" : 0.0,
                      "hits" : [ ]