Add latitude_true_scale to ccrs.LambertCylindrical

[shoyer]

This allows for plotting other popular cylindrical projections (e.g., Gall-Peters)

Fixes #1098

Example usage:

import matplotlib.pyplot as plt
import cartopy.crs as ccrs

plt.figure(figsize=(9.42477796077, 6))
ax = plt.axes(projection=ccrs.LambertCylindrical(latitude_true_scale=45))
ax.coastlines(resolution='110m')
ax.gridlines()

[CLAassistant]

All committers have signed the CLA.

[shoyer]

I think the tests will need to be updated to add new cached images. Is that something I can do, or that happens automatically?

[greglucas]

You can/should update images on your end.

See here for a directory of where it is looking for them: https://github.com/SciTools/cartopy/actions/runs/18792338970/job/53625345081?pr=2588#step:9:206
I typically grab the result produced from CI linux runners and then put that in the spot it is expecting them in the repo renamed appropriately.
https://github.com/SciTools/cartopy/actions/runs/18792338970?pr=2588#artifacts

[greglucas]

Should we actually create a different class GallPeters with a fixed lat_ts=45 and/or a CylindricalEqualArea superclass that takes the new keyword argument. It looks like the Lambert version is specifically for lat_ts=0
https://proj.org/en/stable/operations/projections/cea.html