fix: Pydantic validation error with list-type metadata in vector search (#3797) (#4173)

# Fix for Issue #3797

## Problem
Vector store search failed with Pydantic ValidationError when chunk
metadata contained list-type values.

**Error:**
```
ValidationError: 3 validation errors for VectorStoreSearchResponse
attributes.tags.str: Input should be a valid string
attributes.tags.float: Input should be a valid number
attributes.tags.bool: Input should be a valid boolean
```

**Root Cause:**
- `Chunk.metadata` accepts `dict[str, Any]` (any type allowed)
- `VectorStoreSearchResponse.attributes` requires `dict[str, str | float
| bool]` (primitives only)
- Direct assignment at line 641 caused validation failure for
non-primitive types

## Solution

Added utility function to filter metadata to primitive types before
creating search response.


## Impact

**Fixed:**
- Vector search works with list metadata (e.g., `tags: ["transformers",
"gpu"]`)
- Lists become searchable as comma-separated strings
- No ValidationError on search responses

**Preserved:**
- Full metadata still available in `VectorStoreContent.metadata`
- No API schema changes
- Backward compatible with existing primitive metadata

**Affected:**
All vector store providers using `OpenAIVectorStoreMixin`: FAISS,
Chroma, Qdrant, Milvus, Weaviate, PGVector, SQLite-vec

## Testing


tests/unit/providers/vector_io/test_vector_utils.py::test_sanitize_metadata_for_attributes

---------

Co-authored-by: Ashwin Bharambe <ashwin.bharambe@gmail.com>
Co-authored-by: Francisco Arceo <arceofrancisco@gmail.com>

docs/static/llama-stack-spec.yaml

@@ -8883,9 +8883,21 @@ components:
           title: Object
           default: vector_store.file
         attributes:
-          additionalProperties: true
+          additionalProperties:
+            anyOf:
+            - type: string
+              maxLength: 512
+            - type: number
+            - type: boolean
+            title: string | number | boolean
+          propertyNames:
+            type: string
+            maxLength: 64
           type: object
+          maxProperties: 16
           title: Attributes
+          description: Set of 16 key-value pairs that can be attached to an object. This can be useful for storing additional information about the object in a structured format, and querying for objects via API or the dashboard. Keys are strings with a maximum length of 64 characters. Values are strings with a maximum length of 512 characters, booleans, or numbers.
+          x-oaiTypeLabel: map
         chunking_strategy:
           oneOf:
           - $ref: '#/components/schemas/VectorStoreChunkingStrategyAuto'