Investigate memory leak in HDF5Data

When opening many instances of HDF5Data of the same file. A memory leak appears.


```python

import time
import gc
from dcnum.read import HDF5Data

path = "2025-02-09_09.46_M003_Reference_30000.rtdc"

while True:
    time.sleep(0.1)
    with HDF5Data(path):
        pass
    gc.collect()

```

https://dcor.mpl.mpg.de/dataset/naiad-reference-data