Fix typescript trace bugs (#1275)

Fixes #1274 
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> [!IMPORTANT]
> Fix TypeScript tracing bugs in `BamlCtxManager` by handling undefined
responses and ensuring proper return values.
> 
>   - **Behavior**:
> - Fix `span.finish` in `BamlCtxManager` to handle undefined `response`
by defaulting to an empty object.
> - Ensure `ctx.run` returns the result in `traceFnSync` and
`traceFnAsync` methods of `BamlCtxManager`.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=BoundaryML%2Fbaml&utm_source=github&utm_medium=referral)<sup>
for 8faf23e. It will automatically
update as commits are pushed.</sup>

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Co-authored-by: aaronvg <aaron@boundaryml.com>

engine/language_client_typescript/async_context_vars.js

@@ -51,7 +51,7 @@ class BamlCtxManager {
             return;
         }
         try {
-            span.finish(response, manager);
+            span.finish(response === undefined ? null : response, manager);
         }
         catch (e) {
             console.error('BAML internal error', e);
@@ -78,7 +78,7 @@ class BamlCtxManager {
                 [`arg${i}`]: arg, // generic way to label args
             }), {});
             const [mng, span] = this.startTrace(name, params);
-            this.ctx.run(mng, () => {
+            return this.ctx.run(mng, () => {
                 try {
                     const response = func(...args);
                     this.endTrace(span, response);
@@ -99,7 +99,7 @@ class BamlCtxManager {
                 [`arg${i}`]: arg, // generic way to label args
             }), {});
             const [mng, span] = this.startTrace(name, params);
-            await this.ctx.run(mng, async () => {
+            return await this.ctx.run(mng, async () => {
                 try {
                     const response = await func(...args);
                     this.endTrace(span, response);

engine/language_client_typescript/typescript_src/async_context_vars.ts

@@ -57,7 +57,7 @@ export class BamlCtxManager {
       return
     }
     try {
-      span.finish(response, manager)
+      span.finish(response === undefined ? null : response, manager)
     } catch (e) {
       console.error('BAML internal error', e)
     }
@@ -89,7 +89,7 @@ export class BamlCtxManager {
         {},
       )
       const [mng, span] = this.startTrace(name, params)
-      this.ctx.run(mng, () => {
+      return this.ctx.run(mng, () => {
         try {
           const response = func(...args)
           this.endTrace(span, response)
@@ -113,7 +113,7 @@ export class BamlCtxManager {
         {},
       )
       const [mng, span] = this.startTrace(name, params)
-      await this.ctx.run(mng, async () => {
+      return await this.ctx.run(mng, async () => {
         try {
           const response = await func(...args)
           this.endTrace(span, response)