fix(@langchain/classic): add langsmith as external dependency (#9596)

Author: christian-bromann

.changeset/hungry-planets-brush.md

@@ -0,0 +1,5 @@
+---
+"@langchain/classic": patch
+---
+
+fix(@langchain/classic): add langsmith as external dependency

libs/langchain-classic/tsdown.config.ts

@@ -7,6 +7,7 @@ import {
 } from "@langchain/build";
 
 export default getBuildConfig({
+  external: ["langsmith", "eventemitter3"],
   entry: [
     "./src/index.ts",
     "./src/load/index.ts",