Error due to removal of `get_cmap` in matplotlib 3.9

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PolyFuzz is being installed as a transitive dependency, and I'm getting the following error due to the removal of `matplotlib.cm.get_cmap` in matplotlib 3.9.

```
/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/polyfuzz/__init__.py:1: in
from .polyfuzz import PolyFuzz
/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/polyfuzz/polyfuzz.py:9: in
from polyfuzz.metrics import precision_recall_curve, visualize_precision_recall
/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/polyfuzz/metrics.py:8: in
from matplotlib.cm import get_cmap
E ImportError: cannot import name 'get_cmap' from 'matplotlib.cm' (/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/matplotlib/cm.py)
```

The removal is described in https://matplotlib.org/stable/api/prev_api_changes/api_changes_3.9.0.html#removals, and the suggested fix is as follows:

> use `matplotlib.colormaps[name]` instead if you have a [str](https://docs.python.org/3/library/stdtypes.html#str). Use [matplotlib.cm.ColormapRegistry.get_cmap](https://matplotlib.org/stable/api/cm_api.html#matplotlib.cm.ColormapRegistry.get_cmap) if you have a [str](https://docs.python.org/3/library/stdtypes.html#str), [None](https://docs.python.org/3/library/constants.html#None) or a [matplotlib.colors.Colormap](https://matplotlib.org/stable/api/_as_gen/matplotlib.colors.Colormap.html#matplotlib.colors.Colormap) object that you want to convert to a [Colormap](https://matplotlib.org/stable/api/_as_gen/matplotlib.colors.Colormap.html#matplotlib.colors.Colormap) object.

Start in polyfuzz/metrics.py, where the traceback identifies the removed matplotlib.cm.get_cmap import, and read the linked Matplotlib 3.9 API-removal guidance. Verify that PolyFuzz imports successfully with Matplotlib 3.9 and that the existing metrics behavior remains intact.

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