List vector stores

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      "object": "vector_store",
      "created_at": 1711644800,
      "name": "product-docs",
      "usage_bytes": 1024000,
      "file_counts": {
        "in_progress": 0,
        "completed": 3,
        "failed": 0,
        "cancelled": 0,
        "total": 3
      },
      "status": "completed",
      "last_active_at": 1711731200,
      "expires_after": null,
      "expires_at": null,
      "metadata": {}
    }
  ],
  "first_id": "vs_abc123def456",
  "last_id": "vs_abc123def456",
  "has_more": false
}