Add negentropy support to executor

packages/net/src/target/Echo.ts

@@ -0,0 +1,16 @@
+import {Emitter} from '@welshman/lib'
+import type {Message} from '../Socket'
+
+export class Echo extends Emitter {
+  get connections() {
+    return []
+  }
+
+  send(...payload: Message) {
+    this.emit(...payload)
+  }
+
+  cleanup = () => {
+    this.removeAllListeners()
+  }
+}