Figure.choropleth: Validate the input data type and the column name

[seisman]

As shown by the example below, passing an invalid column leads to a segmentation fault:

In [2]: import geopandas
   ...: import pygmt
   ...: world = geopandas.read_file(
   ...:     "https://naciscdn.org/naturalearth/110m/cultural/ne_110m_admin_0_countries.zip"
   ...: )
   ...: world["POP_EST"] *= 1e-6  # Population in millions
   ...: fig = pygmt.Figure()
   ...: fig.basemap(region=[-19.5, 53, -38, 37.5], projection="M15c", frame=True)
   ...: pygmt.makecpt(cmap="bilbao", series=(0, 270, 10), reverse=True)
   ...: fig.choropleth(world, column="invalid", pen="0.3p,gray10")
   ...: fig.colorbar(frame=True)
   ...: fig.show()
zsh: segmentation fault  ipython

This PR checks the input data type and also check if the specified column exists in the geo-like objects.

[Copilot]

Pull request overview

Adds early validation to Figure.choropleth to prevent invalid inputs and column names from causing segmentation faults.

Changes:

• Validates supported data types and column names.
• Excludes geometry columns from attribute validation.
• Adds regression tests for invalid inputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Summary
pygmt/src/choropleth.py	Adds input and column validation; attribute-less geo-like objects still require column validation handling.
pygmt/tests/test_choropleth.py	Adds tests for invalid columns and data types.

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