[BUG] Prometheus query API does not support scalar

What is the bug?
Prometheus query API does not support scalar result type

How can one reproduce the bug?
Steps to reproduce the behavior:

1. add prometheus data source
2. run query

❯ curl -X 'POST' -H 'Content-Type:application/json' --data-binary '{
  "query": "scalar(count(up))",
  "language": "PROMQL",
  "options": {
    "queryType": "instant",
    "time": "1773874502"
  }
}' --insecure -A 'kulala.nvim/5.3.4' 'localhost:9200/_plugins/_directquery/_query/my_prometheus'
{
  "status": 500,
  "error": {
    "type": "MismatchedInputException",
    "reason": "There was internal problem at backend",
    "details": "Cannot construct instance of `org.opensearch.sql.directquery.transport.model.datasource.PrometheusResult$PrometheusResultItem` (although at least one Creator exists): no int/Int-argument constructor/factory method to deserialize from Number value (1773874502)\n at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 32] (through reference chain: org.opensearch.sql.directquery.transport.model.datasource.PrometheusResult[\"result\"]-\u003ejava.util.ArrayList[0])"
  }
}%

What is the expected behavior?
should not have 500 error

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22] 87067f11dd984cf64dbcecf0921b8ad15bac44e4
• Plugins

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Do you have any additional context?
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