private static MappedFields convertToLowercase(MappedFields mappedFields) {
    if (mappedFields == null) {
      return null;
    }
    return MappedFields.of(convertToLowercase(mappedFields.fields()));
  }
Create a new NameMapping with the same names but converted to lowercase.

@param nameMapping The original NameMapping, potentially containing non-lowercase characters
amoro-format-mixed/amoro-mixed-trino/src/main/java/org/apache/amoro/trino/unkeyed/IcebergPageSourceProvider.java