Save flatten DDB model instead of DATA json

[osipovartem]

• Flattened session and query writes to DynamoDB by storing model fields as individual attributes instead of a JSON blob, enabling filtering on columns.

{
  "query_hash_version": 1,
  "Entity": "query",
  "warehouse_type": "EMBUCKET",
  "query_id": "019b9a21-cdee-7103-b582-7ff0ed921b4c",
  "database_name": "embucket",
  "end_time": "2026-01-07T20:24:27.879777452Z",
  "session_id": "609460f3-322f-4e76-bf31-c1af6a6e38e0",
  "schema_name": "public",
  "execution_time": 2553,
  "start_time": "2026-01-07T20:24:25.326438536Z",
  "query_hash": "558958833988661941",
  "execution_status": "Success",
  "SK": "1767817465326",
  "query_metrics": [
    {
      "metrics": [
        {
          "name": "start_timestamp",
          "partition": {
            "$serde_json::private::Number": "0"
          },
          "value": {
            "$serde_json::private::Number": "1767817466770622315"
          },
          "labels": {},
          "display": "2026-01-07 20:24:26.770622315 UTC"
        },
        {
          "name": "end_timestamp",
          "partition": {
            "$serde_json::private::Number": "0"
          },
          "value": {
            "$serde_json::private::Number": "1767817467879269378"
          },
          "display": "2026-01-07 20:24:27.879269378 UTC",
          "labels": {}
        }
        ...
  ],
  "PK": "QUERY#2026-01-07",
  "request_id": "4441960e-35eb-44f5-b949-924954ce2f92",
  "query_text": "SELECT * FROM embucket.tpch.t1 ORDER BY a,b,c;"
}