[FEATURE] Support non-streaming mode for OpenAI model

[nandateja]

Problem Statement

I would like Strands to support non-streaming mode for OpenAI and compatible servers

Currently, when invoking any OpenAI compatible server with non-streaming mode, we encounter an error:

`model = OpenAIModel(
client_args={
"api_key" : <API_KEY>,
"base_url" : <BASE_URL>
},
model_id=<MODEL_ID>,
params={
"max_tokens": 1000,
"temperature": 0.7,
}
)

agent = Agent(model=model)
response = agent("What is 2+2")`

UnboundLocalError: cannot access local variable 'choice' where it is not associated with a value

It would be great if we add support similar to Bedrock where non streaming mode is supported

Proposed Solution

We can follow similar to Bedrock approach:

sdk-python/src/strands/models/bedrock.py

Line 371 in cc5be12

def _convert_non_streaming_to_streaming(self, response: dict[str, Any]) -> Iterable[StreamEvent]:

Use Case

To support any OpenAI models or Agentic usecases which doesn't need streaming support

Alternatives Solutions

No response

Additional Context

No response