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/providers/inline/inference/vllm/vllm.py

@@ -582,6 +582,7 @@ class VLLMInferenceImpl(Inference, ModelsProtocolPrivate):
                     tool_name=t.function.name,
                     # vLLM function args come back as a string. Llama Stack expects JSON.
                     arguments=json.loads(t.function.arguments),
+                    arguments_json=t.function.arguments,
                 )
                 for t in vllm_message.tool_calls
             ],