Remove deprecation warnings

There are a couple currently triggered:

mednet/data/split.py:69: DeprecationWarning: 'importlib.abc.Traversable' is deprecated and slated for removal in Python 3.14

mednet/engine/saliency/viewer.py:95: MatplotlibDeprecationWarning: The get_cmap function was deprecated in Matplotlib 3.7 and will be removed two minor releases later. Use ``matplotlib.colormaps[name]`` or ``matplotlib.colormaps.get_cmap(obj)`` instead.