Avoid unwanted exception chaining when running async tool in sync context (#9092)

Running async tool under sync context (require `settings.allow_tool_async_sync_conversion`) is handled by `Tool._run_async_in_sync`. If there's no running event loop, we used to run the coroutine directly when handling the `RuntimeError` raised by `asyncio.get_running_loop()`. This resulted in exception chaining, where the error raised by the tool will be chained with the `RuntimeError` raised by `asyncio`. Since the result will be passed to the LM as tool call result, such behavior is regarded as unnecessary leak of implementation detail, and will diverge the result of running with `async` and in sync. Move the real call outside of the `except` block will resolve the problem.

## Before

```
Execution error in retrieve: 
Traceback (most recent call last):
  File ".venv\Lib\site-packages\dspy\adapters\types\tool.py", line 167, in _run_async_in_sync
    loop = asyncio.get_running_loop()
RuntimeError: no running event loop

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".venv\Lib\site-packages\dspy\predict\react.py", line 111, in forward
    trajectory[f"observation_{idx}"] = self.tools[pred.next_tool_name](**pred.next_tool_args)
                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\dspy\utils\callback.py", line 326, in sync_wrapper
    return fn(instance, *args, **kwargs)
  File ".venv\Lib\site-packages\dspy\adapters\types\tool.py", line 176, in __call__
    result = self.func(**parsed_kwargs)
  File "src\retrieval\tool.py", line 169, in retrieve
    result = run_request(kwargs)
             ~~~~~~~~~~~^^^^^^^^
ValueError: Invalid request
```

## After

```
Execution error in retrieve: 
Traceback (most recent call last):
  File ".venv\Lib\site-packages\dspy\predict\react.py", line 111, in forward
    trajectory[f"observation_{idx}"] = self.tools[pred.next_tool_name](**pred.next_tool_args)
                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\dspy\utils\callback.py", line 326, in sync_wrapper
    return fn(instance, *args, **kwargs)
  File ".venv\Lib\site-packages\dspy\adapters\types\tool.py", line 176, in __call__
    result = self.func(**parsed_kwargs)
  File "src\retrieval\tool.py", line 169, in retrieve
    result = run_request(kwargs)
             ~~~~~~~~~~~^^^^^^^^
ValueError: Invalid request
```

Author: stevapple

dspy/adapters/types/tool.py

@@ -166,8 +166,11 @@ def _run_async_in_sync(self, coroutine):
         try:
             loop = asyncio.get_running_loop()
         except RuntimeError:
-            return asyncio.run(coroutine)
+            # Run the coroutine outside of "except" block to avoid propagation
+            loop = None
 
+        if loop is None:
+            return asyncio.run(coroutine)
         return loop.run_until_complete(coroutine)
 
     @with_callbacks