cmd, consensus: add option to disable mmap for DAG caches/datasets (#20484)

* cmd, consensus: add option to disable mmap for DAG caches/datasets

* consensus: add benchmarks for mmap with/with lock

cmd/geth/retesteth.go

@@ -387,11 +387,13 @@ func (api *RetestethAPI) SetChainParams(ctx context.Context, chainParams ChainPa
 		inner = ethash.NewFaker()
 	case "Ethash":
 		inner = ethash.New(ethash.Config{
-			CacheDir:       "ethash",
-			CachesInMem:    2,
-			CachesOnDisk:   3,
-			DatasetsInMem:  1,
-			DatasetsOnDisk: 2,
+			CacheDir:         "ethash",
+			CachesInMem:      2,
+			CachesOnDisk:     3,
+			CachesLockMmap:   false,
+			DatasetsInMem:    1,
+			DatasetsOnDisk:   2,
+			DatasetsLockMmap: false,
 		}, nil, false)
 	default:
 		return false, fmt.Errorf("unrecognised seal engine: %s", chainParams.SealEngine)