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]>

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

@@ -131,6 +131,10 @@ class HyperP2PStreamMultiplex extends EventEmitter {
     return this.snapshot()
   }
 
+  exportState () {
+    return this.toJSON()
+  }
+
   openStreamBatch (ids) {
     if (!Array.isArray(ids)) throw new Error('ids array required')
     return ids.map((id) => this.openStream(id))