Slow to export

## Read and complete the full issue template

Do not randomly delete sections. They are here for a reason.

**Do you want to request a *feature* or report a *bug*?**
- [x] Bug
- [ ] Feature
- [ ] Question

**Did you test against the latest CI build?**
- [x] Yes
- [ ] No

If you answered `No`, please test with [the latest development build](https://ci.appveyor.com/project/ClosedXML/ClosedXML/branch/develop/artifacts) first.

**Version of ClosedXML**

v 0.101.0

**Version of ClosedXML.Report**

v 0.2.8

**What is the current behavior?**

I have an Excel template that I turn into a Stream so the data from a grid can export to the template using ClosedXML.Report. I have an array[18000] with about 18000 rows and 8 columns, all just strings from a datagrid. When I export it using ClosedXML, it takes like 5-10mins before it shows me the "Save To" location popup, and the file size is only like 1.3mb. Whereas when the array is 1000 rows, it only takes a couple seconds. I'm not sure if using the ClosedXML.Report for the template has to do with the performance or not, but it does get stuck after template.Generate();

**What is the expected behavior or new feature?**

I was using ClosedXML version 0.95.0 and I expected the performance to increase, but its roughly the same.

**Is this a regression from the previous version?**

See above

## Reproducibility
**This is an important section. Read it carefully. Failure to do so will cause a 'RTFM' comment.**

Without a code sample, it is unlikely that your issue will get attention. Don't be lazy. Do the effort and assist the developers to reproduce your problem. Code samples should be [minimal complete and verifiable](https://stackoverflow.com/help/mcve). Sample spreadsheets should be attached whenever applicable. Remove sensitive information.

**Code to reproduce problem:**
```c#

using ClosedXML.Excel;
using ClosedXML.Report;

var template = new XLTemplate(StreamTemplate); // this is the Excel Template I created, type Stream
SomeArray[] data; // 18000+ rows of data from a grid
template.AddVariable("VariableName", data) // variable is from the Excel template
template.Generate(); // when I debug and step over here, this is where it takes a long time before the 'File save to location' pops up
IXLWorkbook workbook = template.Workbook;
MemoryStream ExcelStream = new();
workbook.SaveAs(ExcelStream);

```

- [ ] I attached a sample spreadsheet. (You can drag files on to this issue)

Thanks!