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]>

state-crdts/hyper-p2p-crdt-version-vector/index.js

@@ -79,6 +79,10 @@ class HyperP2PCrdtVersionVector extends EventEmitter {
     return this.snapshot()
   }
 
+  isEmpty () {
+    return Object.keys(this.snapshot()).length === 0
+  }
+
   get (peer) {
     return this._clock.get(assertPeer(peer)) || 0
   }