The cost of merged cell filling is extremely high for LINQ queries. #837

Enabling merged cell filling (FillMergedCells = true) has a significant performance impact on LINQ queries, even when using simple operations like .Skip() or .First().

In our case, after setting:

var a = MiniExcel.Query(@"D:\Test1,000,000x10.xlsx", configuration: new OpenXmlConfiguration() { FillMergedCells = true }).First();

went from 56ms to over 9000ms.