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/log.py

@@ -32,6 +32,7 @@ CATEGORIES = [
     "tools",
     "client",
     "telemetry",
+    "openai_responses",
 ]
 
 # Initialize category levels with default level