curl --request GET \
  --url https://api-west.millis.ai/agents/{agent_id}/call-histories

{
  "items": [
    {
      "agent_config": {},
      "duration": 123,
      "ts": 123,
      "chat": "<string>",
      "chars_used": 123,
      "session_id": "<string>",
      "cost_breakdown": [
        {}
      ],
      "agent_id": "<string>",
      "call_id": "<string>",
      "voip": {},
      "recording": {},
      "metadata": {},
      "function_calls": [
        {}
      ],
      "call_status": "<string>"
    }
  ],
  "pagination": {
    "success": true
  }
}