fix: direct client pydantic type casting (#1145)

# What does this PR do?
- Closes #1142 
- Root cause is due to having `Union[str, AgenToolGroupWithArgs]`

## Test Plan
- Test with script described in issue. 

- Print out final converted pydantic object
<img width="1470" alt="image"
src="https://github.com/user-attachments/assets/15dc9cd0-f37a-4b91-905f-3fe4f59a08c6"
/>


[//]: # (## Documentation)

llama_stack/strong_typing/classdef.py

@@ -203,7 +203,7 @@ def schema_to_type(schema: Schema, *, module: types.ModuleType, class_name: str)
             if type_def.default is not dataclasses.MISSING:
                 raise TypeError("disallowed: `default` for top-level type definitions")
 
-            setattr(type_def.type, "__module__", module.__name__)
+            type_def.type.__module__ = module.__name__
             setattr(module, type_name, type_def.type)
 
     return node_to_typedef(module, class_name, top_node).type