Update colormap registration

[ns-rse]

Matplotlib 3.9 will see the deprecation of matplotlib.cm.register_cmap() which we currently use as plt.register_cmap() in topostats/init.py...

"""Topostats."""

from importlib.metadata import version

import matplotlib.pyplot as plt
import snoop

from .logs.logs import setup_logger
from .theme import Colormap

LOGGER = setup_logger()

release = version("topostats")
__version__ = ".".join(release.split("."[:2]))

plt.register_cmap(cmap=Colormap("nanoscope").get_cmap())
plt.register_cmap(cmap=Colormap("gwyddion").get_cmap())

Whilst the function name has been deprecated the functionality hasn't and the commit that covers this details what function to use instead...

Removal of top-level cmap registration and access functions in ``mpl.cm``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As part of the `multi-step refactoring of colormap registration
<https://github.com/matplotlib/matplotlib/issues/20853>`_, the following functions have
been removed:

- ``matplotlib.cm.get_cmap``; use ``matplotlib.colormaps[name]`` instead if you
  have a `str`.

  Use `matplotlib.cm.ColormapRegistry.get_cmap` if you have a `str`, `None` or a
  `matplotlib.colors.Colormap` object that you want to convert to a `.Colormap`
  object.
- ``matplotlib.cm.register_cmap``; use `matplotlib.colormaps.register
  <.ColormapRegistry.register>` instead.
- ``matplotlib.cm.unregister_cmap``; use `matplotlib.colormaps.unregister
  <.ColormapRegistry.unregister>` instead.
- ``matplotlib.pyplot.register_cmap``; use `matplotlib.colormaps.register
  <.ColormapRegistry.register>` instead.

The `matplotlib.pyplot.get_cmap` function will stay available for backward
compatibility.

I think the replacement required is therefore...

from matplotlib import colormaps

colormaps.register(cmap=Colormap("nanoscope").get_cmap())
colormaps.register(cmap=Colormap("gwyddion").get_cmap())