Standardization does not preserve metadata of nested fields

[yruslan]

Describe the bug

Standardization keeps metadata of root fields, but does not preserve metadata of nested fields.

To Reproduce

Run standardization of a dataframe with a following schema:

{
  "type": "struct",
  "fields": [
    {
      "name": "STRING_FIELD",
      "type": "string",
      "nullable": true,
      "metadata": {
        "maxLength": 8
      }
    },
    {
      "name": "NESTED_STRUCT",
      "type": {
        "type": "struct",
        "fields": [
          {
            "name": "NESTED_STRING",
            "type": "string",
            "nullable": true,
            "metadata": {
              "maxLength": 5
            }
          }
        ]
      }
    }
  ]
}

The result will look like this (nested field's metadata is lost):

{
  "type": "struct",
  "fields": [
    {
      "name": "STRING_FIELD",
      "type": "string",
      "nullable": true,
      "metadata": {
        "maxLength": 8
      }
    },
    {
      "name": "NESTED_STRUCT",
      "type": {
        "type": "struct",
        "fields": [
          {
            "name": "NESTED_STRING",
            "type": "string",
            "nullable": true,
            "metadata": { }
          }
        ]
      }
    }
  ]
}

• STRING_FIELD has metadata retained.
• NESTED_STRING has list metadata field "maxLength": 5

Expected behavior

Standardization should preserve all metadata.

Screenshots

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Additional context

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