Add isEmpty() helpers across all modules with clearable state.

Seventh expansion pass: domain-specific isEmpty() after moduleSnapshot on every module that has clearAll(), using existing count/snapshot helpers (async variants for temporal, spatial, semantic-vector, and reactive-state indexes).

Co-authored-by: Cursor <[email protected]>

messaging-pubsub/hyper-p2p-qos-topic/index.js

@@ -137,6 +137,12 @@ class HyperP2PQosTopic extends EventEmitter {
     return this.snapshot()
   }
 
+  isEmpty () {
+    const s = this.snapshot()
+    return s.channels.length === 0 && s.handlers === 0 &&
+      Object.values(s.queueDepths).every((n) => n === 0)
+  }
+
   _onGossip (data) {
     if (!data || data.type !== 'qos-publish') return
     this._stats.gossipIn++