### 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/test/java/org/elasticsearch/action/search/SearchResponseTests.java
"reason": "corrupt index"
                            }
                          }
                        ]
                      },
                      "cluster_0": {
                        "status": "partial",
                        "indices": "foo,bar*",
                        "took": 1000,
                        "timed_out": false,
                        "_shards": {
                          "total": 5,
                          "successful": 4,
                          "skipped": 1,
                          "failed": 1
                        },
                        "failures": [
                          {
                            "shard": -1,
                            "index": null,
                            "reason": {
                              "type": "illegal_state_exception",
                              "reason": "corrupt index"
                            }
                          }
                        ]
                      }
                    }
                  },
                  "hits": {