simplify with preserve_topology=True difference for MultiLineString between 3.12.1 and 3.12.2

[theroggy]

A CI test of mine started failing for 3.12.2 versus 3.12.1, and I wondered what the correct expected behaviour is...
Reference: pygeoops/pygeoops#97

I suppose the change in behaviour is linked to this PR: #1012

There difference is in the result of simplify with preserve_topology=True for MultiLineString geometries in 3.12.2 compared to 3.12.1.

With 3.12.1, the input linestring left, the result of simplify to the right:

With 3.12.2, the input linestring left, the result of simplify to the right:

Script to reproduce:

from matplotlib import pyplot as plt
import shapely
import shapely.plotting as plotter

# Prepare test data
input_wkt = "MULTILINESTRING ((0 10, 10 10, 10 0), (10 10, 11 0, 10 0))"
input_geom = shapely.from_wkt(input_wkt)

# Simplify the input
result = shapely.simplify(input_geom, tolerance=2, preserve_topology=True)

# Plot input and result
fig, ax = plt.subplots(ncols=2)
colors = ["red", "blue"]
for index, line in enumerate(input_geom.geoms):
    plotter.plot_line(line, ax=ax[0], add_points=True, color=colors[index])
    ax[0].set_aspect("equal")
for index, line in enumerate(result.geoms):
    plotter.plot_line(line, ax=ax[1], add_points=True, color=colors[index])
    ax[1].set_aspect("equal")

plt.show()

[dr-jts]

The new behaviour is correct. TopologyPreservingSimplifier keeps the linestrings separate, in order to preserve the topology.