Large slowdown of elastix_registration_method after reading a DICOM series

Konstantinos (@ntatsisk) discovered that when a reasonably large DICOM series is read by `itk.imread`, it very much slows down a subsequent `itk.elastix_registration_method` call, _even_ when the DICOM series is not used!

We did locally replace `itk.imread` by a "dummy" `dummy_imread`, as below here, and the negative speed effect was still there. So apparently it's something about the `reader.Update()` taking resources away.

```
def dummy_imread(filename):
names_generator = itk.GDCMSeriesFileNames.New()
names_generator.SetDirectory(f"{filename}")
series_uid = names_generator.GetSeriesUIDs()
reader = itk.ImageSeriesReader[itk.Image[itk.F, 3]].New()
reader.SetFileNames(filenames)
reader.Update()
```

The registration was of the following form, so it did not use DICOM at all:

```
fixed = itk.imread("test.mhd", itk.F)
parameter_object = itk.ParameterObject.New()
parameter_object.ReadParameterFile('rigid.txt')
parameter_object.SetParameter(0, "MaximumNumberOfIterations", "1")
starttime = time.time()
itk.elastix_registration_method(fixed, fixed, parameter_object=parameter_object, log_to_console=True)
print(time.time() - starttime)
```

The slowdown can be really large. It seems to depend on the number of files of the DICOM series, but the duration of a registration can go up from 8 seconds to more than 40 seconds. The problem was encountered when reading a series of 408 T2 weighted *.dcm files from https://www.kaggle.com/competitions/rsna-miccai-brain-tumor-radiogenomic-classification/data Running on Windows.

Is this a known issue? Do you have any suggestion how to further narrow the reproducing example, and how to find the cause of the issue?