[memory refactor][2/n] Update faiss and make it pass tests (#830)

See https://github.com/meta-llama/llama-stack/issues/827 for the broader
design.

Second part:

- updates routing table / router code 
- updates the faiss implementation


## Test Plan

```
pytest -s -v -k sentence test_vector_io.py --env EMBEDDING_DIMENSION=384
```

llama_stack/providers/registry/agents.py

@@ -33,8 +33,8 @@ def available_providers() -> List[ProviderSpec]:
             api_dependencies=[
                 Api.inference,
                 Api.safety,
-                Api.memory,
-                Api.memory_banks,
+                Api.vector_io,
+                Api.vector_dbs,
                 Api.tool_runtime,
                 Api.tool_groups,
             ],