cmd/utils: avoid large alloc in --dev mode (#22949)

* cmd/utils: avoid 1Gb alloc in --dev mode

* cmd/geth: avoid 512Mb alloc in genesis query tests

cmd/utils/flags.go

@@ -1234,6 +1234,9 @@ func SetNodeConfig(ctx *cli.Context, cfg *node.Config) {
 	if ctx.GlobalIsSet(KeyStoreDirFlag.Name) {
 		cfg.KeyStoreDir = ctx.GlobalString(KeyStoreDirFlag.Name)
 	}
+	if ctx.GlobalIsSet(DeveloperFlag.Name) {
+		cfg.UseLightweightKDF = true
+	}
 	if ctx.GlobalIsSet(LightKDFFlag.Name) {
 		cfg.UseLightweightKDF = ctx.GlobalBool(LightKDFFlag.Name)
 	}
@@ -1647,6 +1650,7 @@ func SetEthConfig(ctx *cli.Context, stack *node.Node, cfg *ethconfig.Config) {
 		if !ctx.GlobalIsSet(NetworkIdFlag.Name) {
 			cfg.NetworkId = 1337
 		}
+		cfg.SyncMode = downloader.FullSync
 		// Create new developer account or reuse existing one
 		var (
 			developer  accounts.Account