fix: Updating ToolCall.arguments to allow for json strings that can be decoded on client side (#1685)

### What does this PR do?

Currently, `ToolCall.arguments` is a `Dict[str, RecursiveType]`.
However, on the client SDK side -- the `RecursiveType` gets deserialized
into a number ( both int and float get collapsed ) and hence when params
are `int` they get converted to float which might break client side
tools that might be doing type checking.

Closes: https://github.com/meta-llama/llama-stack/issues/1683

### Test Plan
Stainless changes --
https://github.com/meta-llama/llama-stack-client-python/pull/204
```
pytest -s -v --stack-config=fireworks tests/integration/agents/test_agents.py  --text-model meta-llama/Llama-3.1-8B-Instruct
```

llama_stack/models/llama/datatypes.py

@@ -47,7 +47,14 @@ RecursiveType = Union[Primitive, List[Primitive], Dict[str, Primitive]]
 class ToolCall(BaseModel):
     call_id: str
     tool_name: Union[BuiltinTool, str]
-    arguments: Dict[str, RecursiveType]
+    # Plan is to deprecate the Dict in favor of a JSON string
+    # that is parsed on the client side instead of trying to manage
+    # the recursive type here.
+    # Making this a union so that client side can start prepping for this change.
+    # Eventually, we will remove both the Dict and arguments_json field,
+    # and arguments will just be a str
+    arguments: Union[str, Dict[str, RecursiveType]]
+    arguments_json: Optional[str] = None
 
     @field_validator("tool_name", mode="before")
     @classmethod

llama_stack/models/llama/llama3/chat_format.py

@@ -12,6 +12,7 @@
 # the top-level of this source tree.
 
 import io
+import json
 import uuid
 from dataclasses import dataclass
 from typing import Dict, List, Optional, Tuple
@@ -203,9 +204,10 @@ class ChatFormat:
             # This code tries to handle that case
             if tool_name in BuiltinTool.__members__:
                 tool_name = BuiltinTool[tool_name]
-                tool_arguments = {
-                    "query": list(tool_arguments.values())[0],
-                }
+                if isinstance(tool_arguments, dict):
+                    tool_arguments = {
+                        "query": list(tool_arguments.values())[0],
+                    }
         else:
             builtin_tool_info = ToolUtils.maybe_extract_builtin_tool_call(content)
             if builtin_tool_info is not None:
@@ -229,6 +231,7 @@ class ChatFormat:
                     call_id=call_id,
                     tool_name=tool_name,
                     arguments=tool_arguments,
+                    arguments_json=json.dumps(tool_arguments),
                 )
             )
             content = ""

llama_stack/models/llama/llama3/template_data.py

@@ -11,11 +11,8 @@
 # top-level folder for each specific model found within the models/ directory at
 # the top-level of this source tree.
 
-from llama_stack.models.llama.datatypes import (
-    BuiltinTool,
-    StopReason,
-    ToolCall,
-)
+
+from llama_stack.models.llama.datatypes import BuiltinTool, StopReason, ToolCall
 
 from .prompt_templates import (
     BuiltinToolGenerator,