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-streams/hyper-p2p-stream-multiplex/index.js

@@ -139,6 +139,10 @@ class HyperP2PStreamMultiplex extends EventEmitter {
     return this.snapshot()
   }
 
+  isEmpty () {
+    return this.snapshot().open === 0
+  }
+
   openStreamBatch (ids) {
     if (!Array.isArray(ids)) throw new Error('ids array required')
     return ids.map((id) => this.openStream(id))