Factor node-system out of start-node

For inits a-la-carte

core/src/main/clojure/xtdb/node.clj

@@ -119,6 +119,27 @@
  (cond-> opts
  (not (ig/find-derived opts parent-k)) (assoc impl-k {})))
 
+(defn node-system [opts]
+ (-> (into {::node {}
+ :xtdb/allocator {}
+ :xtdb/default-tz nil
+ :xtdb/indexer {}
+ :xtdb.indexer/internal-id-manager {}
+ :xtdb/live-chunk {}
+ :xtdb.indexer/live-index {}
+ :xtdb/ingester {}
+ :xtdb.metadata/metadata-manager {}
+ :xtdb.temporal/temporal-manager {}
+ :xtdb.buffer-pool/buffer-pool {}
+ :xtdb.operator.scan/scan-emitter {}
+ :xtdb.operator/ra-query-source {}
+ ::txp/tx-producer {}}
+ opts)
+ (doto ig/load-namespaces)
+ (with-default-impl :xtdb/log :xtdb.log/memory-log)
+ (with-default-impl :xtdb/object-store :xtdb.object-store/memory-object-store)
+ (doto ig/load-namespaces)))
+
 (defn start-node ^xtdb.node.Node [opts]
  (let [system (-> (into {::node {}
  :xtdb/allocator {}