chore(tests): fix responses and vector_io tests (#3119)

Some fixes to MCP tests. And a bunch of fixes for Vector providers.

I also enabled a bunch of Vector IO tests to be used with
`LlamaStackLibraryClient`

## Test Plan

Run Responses tests with llama stack library client:
```
pytest -s -v tests/integration/non_ci/responses/ --stack-config=server:starter \
   --text-model openai/gpt-4o \
  --embedding-model=sentence-transformers/all-MiniLM-L6-v2 \
  -k "client_with_models"
```

Do the same with `-k openai_client`

The rest should be taken care of by CI.

llama_stack/providers/inline/agents/meta_reference/openai_responses.py

@@ -488,8 +488,12 @@ class OpenAIResponsesImpl:
             # Convert collected chunks to complete response
             if chat_response_tool_calls:
                 tool_calls = [chat_response_tool_calls[i] for i in sorted(chat_response_tool_calls.keys())]
+
+                # when there are tool calls, we need to clear the content
+                chat_response_content = []
             else:
                 tool_calls = None
+
             assistant_message = OpenAIAssistantMessageParam(
                 content="".join(chat_response_content),
                 tool_calls=tool_calls,