feat: Add missing Vector Store Files API surface (#2468)

# What does this PR do?

This adds the ability to list, retrieve, update, and delete Vector Store
Files. It implements these new APIs for the faiss and sqlite-vec
providers, since those are the two that also have the rest of the vector
store files implementation.

Closes #2445 

## Test Plan

### test_openai_vector_stores Integration Tests

There are a number of new integration tests added, which I ran for each
provider as outlined below.

faiss (from ollama distro):

```
INFERENCE_MODEL="meta-llama/Llama-3.2-3B-Instruct" \
llama stack run llama_stack/templates/ollama/run.yaml

LLAMA_STACK_CONFIG=http://localhost:8321 \
pytest -sv tests/integration/vector_io/test_openai_vector_stores.py \
  --embedding-model=all-MiniLM-L6-v2
```

sqlite-vec (from starter distro):

```
llama stack run llama_stack/templates/starter/run.yaml

LLAMA_STACK_CONFIG=http://localhost:8321 \
pytest -sv tests/integration/vector_io/test_openai_vector_stores.py \
  --embedding-model=all-MiniLM-L6-v2
```

### file_search verification tests

I also ensured the file_search verification tests continue to work, both
for faiss and sqlite-vec.

faiss (ollama distro):

```
INFERENCE_MODEL="meta-llama/Llama-3.2-3B-Instruct" \
llama stack run llama_stack/templates/ollama/run.yaml

pytest -sv tests/verifications/openai_api/test_responses.py \
  -k'file_search' \
  --base-url=http://localhost:8321/v1/openai/v1 \
  --model=meta-llama/Llama-3.2-3B-Instruct
```


sqlite-vec (starter distro):

```
llama stack run llama_stack/templates/starter/run.yaml

pytest -sv tests/verifications/openai_api/test_responses.py \
  -k'file_search' \
  --base-url=http://localhost:8321/v1/openai/v1 \
  --model=together/meta-llama/Llama-3.2-3B-Instruct-Turbo
```

---------

Signed-off-by: Ben Browning <bbrownin@redhat.com>

llama_stack/distribution/routers/vector_io.py

@@ -21,7 +21,13 @@ from llama_stack.apis.vector_io import (
     VectorStoreObject,
     VectorStoreSearchResponsePage,
 )
-from llama_stack.apis.vector_io.vector_io import VectorStoreChunkingStrategy, VectorStoreFileObject
+from llama_stack.apis.vector_io.vector_io import (
+    VectorStoreChunkingStrategy,
+    VectorStoreFileContentsResponse,
+    VectorStoreFileDeleteResponse,
+    VectorStoreFileObject,
+    VectorStoreFileStatus,
+)
 from llama_stack.log import get_logger
 from llama_stack.providers.datatypes import HealthResponse, HealthStatus, RoutingTable
 
@@ -279,6 +285,81 @@ class VectorIORouter(VectorIO):
             chunking_strategy=chunking_strategy,
         )
 
+    async def openai_list_files_in_vector_store(
+        self,
+        vector_store_id: str,
+        limit: int | None = 20,
+        order: str | None = "desc",
+        after: str | None = None,
+        before: str | None = None,
+        filter: VectorStoreFileStatus | None = None,
+    ) -> list[VectorStoreFileObject]:
+        logger.debug(f"VectorIORouter.openai_list_files_in_vector_store: {vector_store_id}")
+        # Route based on vector store ID
+        provider = self.routing_table.get_provider_impl(vector_store_id)
+        return await provider.openai_list_files_in_vector_store(
+            vector_store_id=vector_store_id,
+            limit=limit,
+            order=order,
+            after=after,
+            before=before,
+            filter=filter,
+        )
+
+    async def openai_retrieve_vector_store_file(
+        self,
+        vector_store_id: str,
+        file_id: str,
+    ) -> VectorStoreFileObject:
+        logger.debug(f"VectorIORouter.openai_retrieve_vector_store_file: {vector_store_id}, {file_id}")
+        # Route based on vector store ID
+        provider = self.routing_table.get_provider_impl(vector_store_id)
+        return await provider.openai_retrieve_vector_store_file(
+            vector_store_id=vector_store_id,
+            file_id=file_id,
+        )
+
+    async def openai_retrieve_vector_store_file_contents(
+        self,
+        vector_store_id: str,
+        file_id: str,
+    ) -> VectorStoreFileContentsResponse:
+        logger.debug(f"VectorIORouter.openai_retrieve_vector_store_file_contents: {vector_store_id}, {file_id}")
+        # Route based on vector store ID
+        provider = self.routing_table.get_provider_impl(vector_store_id)
+        return await provider.openai_retrieve_vector_store_file_contents(
+            vector_store_id=vector_store_id,
+            file_id=file_id,
+        )
+
+    async def openai_update_vector_store_file(
+        self,
+        vector_store_id: str,
+        file_id: str,
+        attributes: dict[str, Any],
+    ) -> VectorStoreFileObject:
+        logger.debug(f"VectorIORouter.openai_update_vector_store_file: {vector_store_id}, {file_id}")
+        # Route based on vector store ID
+        provider = self.routing_table.get_provider_impl(vector_store_id)
+        return await provider.openai_update_vector_store_file(
+            vector_store_id=vector_store_id,
+            file_id=file_id,
+            attributes=attributes,
+        )
+
+    async def openai_delete_vector_store_file(
+        self,
+        vector_store_id: str,
+        file_id: str,
+    ) -> VectorStoreFileDeleteResponse:
+        logger.debug(f"VectorIORouter.openai_delete_vector_store_file: {vector_store_id}, {file_id}")
+        # Route based on vector store ID
+        provider = self.routing_table.get_provider_impl(vector_store_id)
+        return await provider.openai_delete_vector_store_file(
+            vector_store_id=vector_store_id,
+            file_id=file_id,
+        )
+
     async def health(self) -> dict[str, HealthResponse]:
         health_statuses = {}
         timeout = 1  # increasing the timeout to 1 second for health checks