chore: use persistence setting on server

avoid the whole db.wire part...

src/index.mjs

@@ -1,21 +1,17 @@
 import mosca from 'mosca';
 
 // source: https://github.com/mcollina/mosca/wiki/Mosca-basic-usage
-// source: https://github.com/mcollina/mosca/wiki/Persistence-support
 
 const moscaSettings = {
   port: 1883,
+  persistence: {
+    factory: mosca.persistence.LevelUp,
+    path: 'db',
+  },
 };
 
 const server = new mosca.Server(moscaSettings);
 
-// set up the persistence layer
-const db = new mosca.persistence.LevelUp({
-  path: 'db',
-});
-
-db.wire(server);
-
 const setup = () => {
   console.log('Mosca server is up and running');