Add exportState and moduleSnapshot helpers across all module categories.

Fifth pass: complete measurement modules (sla-budget, histogram-gossip) with moduleSnapshot/toJSON; stats-exporter exportSnapshot; exportState() alias on modules with standard snapshot serialization.

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

network-stack/hyper-p2p-overlay-topology/index.js

@@ -92,6 +92,10 @@ class HyperP2POverlayTopology extends EventEmitter {
     return this.snapshot()
   }
 
+  exportState () {
+    return this.toJSON()
+  }
+
   getStats () {
     return { ...this._stats, degree: this._neighbors.size, protocol: PROTOCOL }
   }