feat(coding-runtime): add managed Pi extension host

tests/unit/pi-worker-pool-process-integration.test.ts

@@ -48,6 +48,10 @@ class ProcessBackedWorker implements PiConversationWorker {
     return this.process.request(command, options);
   }
 
+  send(command: PiRpcCommand): Promise<void> {
+    return this.process.send(command);
+  }
+
   subscribe(listener: (event: PiRpcEvent) => void): () => void {
     return this.process.subscribe(listener);
   }