Add support for world coordinates (WCSAxes)

[HealthyPear]

This PR adds support for a class used in the visualization of astronomical data via astropy.wcs.

These can be plots such as this one, showing radio data of the supernova remnant W49B from the THOR survey:

that can be generated with a snippet such as this one:

from pathlib import Path

import matplot2tikz
import matplotlib.pyplot as plt
from astropy.wcs import WCS
from astropy.io import fits

with fits.open("path/to/a/compatible/file.fits")][0]) as hdul:
    hdu = hdul[0]
    wcs = WCS(hdu.header)
    data = hdu.data

fig, ax = plt.subplots(subplot_kw=dict(projection=wcs))
vmin=data.min()
vmax=data.max()
mappable = ax.imshow(data, vmin=vmin, vmax=vmax, origin='lower', cmap="mako")
ax.grid(color='white', ls='solid', alpha=0.5)
levels = np.linspace(vmin, vmax, 5)
contours = ax.contour(data, levels=levels, colors='white', alpha=0.5)
ax.set(xlabel='Galactic Longitude', ylabel='Galactic Latitude')
cbar = fig.colorbar(mappable, ax=ax, label=hdu.header["BUNIT"])
ax.clabel(contours, fontsize=15, fmt="%.1f")

matplot2tikz.save("test.tex")

Before this PR a warning is generated saying that matplot2tikz does not know how to handle the underlying artist class and the resulting plot when compiled in latex shows as empty.

Changes:

_save.py

• Added support for handling _WCSAxesArtist in the _recurse() function

The _WCSAxesArtist is a placeholder artist from astropy's WCS visualization that has no visible rendering content
By skipping it gracefully, we eliminate the warning while preserving all actual plot content
This approach is consistent with how other placeholder artists (Spines, XAxis, YAxis) are handled

test_wcs_axes.py

• Tests WCS axes with images, grids, colorbars, and contours
• Verifies no warnings about _WCSAxesArtist are generated
• Validates TikZ output contains expected elements
• Gracefully handles environments without astropy installed (uses pytest skip)

[ErwindeGelder]

Thanks for your contribution!

Also thanks for adding the test script. I removed the pytest skip part, because I think it is good to always do the test. I have added astropy to the requirements lists (you already did that for the pyproject.toml, thank you), so the tests run fine.