ci(plot): add plot option to conftest

[langevin-usgs]

Many of the autotest scripts have code for plotting results. This PR establishes a convention for passing in a --plot command line option to pytest, which will cause a plot_output() function to be called.

Checklist of items for pull request

• Replaced section above with description of pull request
• Added new test or modified an existing test
• Ran ruff on new and modified python scripts in .doc, autotests, doc, distribution, pymake, and utils subdirectories.
• Removed checklist items not relevant to this pull request

For additional information see instructions for contributing and instructions for developing.

[wpbonelli]

I remember now that the examples are where we've done this most extensively https://github.com/MODFLOW-USGS/modflow6-examples/blob/develop/autotest/conftest.py

maybe these could be provided by devtools, at least write/run/plot which are generally applicable.

[langevin-usgs]

Good idea to look into supporting the full suite of write/run/plot. It would be nice to have full control over these. For example, it may be nice to manually modify an input file and then be able to check output and plot. A trick for the modflow6 repo will be how to handle the paths, as the models are written/tested in a pytest temp directory.

[mjr-deltares]

This is a nice development, should we at some point ask people to roll this out into 'their' tests, I certainly would like to do that.

[wpbonelli]

@mjr-deltares agreed, yesterday we discussed encouraging people to implement this pattern in their own tests

@langevin-usgs we currently have the --keep option to save a temp dir in a user-specified location — to support the use case you describe, maybe we could consider a --load option which instead of writing the simulation, tries to load the simulation from a specified location?