Add test for species transport model

[ansjsia]

Test the following features of the species transport model:

• Turning on the species transport model
• Checking the mixtures object command list
• Creating a custom mixture with custom species (using the TUI)
• Copying an existing mixture
• Reassigning a cellzone material to a different mixture
• Deleting an existing mixture

Currently, the species transport model cannot be used without resorting to TUI commands due to the following open issues with the settings API:

• Creating/copying mixtures: Mixture/species transport model API should replicate behavior of materials change/create API #2275
• Listing mixtures, species, and properties: List methods for mixtures don't return anything #2277
• Deleting a species from a mixture: Error in deleting species from mixture template (species transport) #2259
• Creating a mixture from an empty dictionary: Creating new mixture with empty dictionary breaks mixture API #2274

[ansjsia]

@dnwillia-work @raph-luc For your consideration in the latest commit. I've renamed the file to test_species_model.py and split it up into multiple tests. I created a fixture such that only one solver instance would be used across all tests, ensuring that we only start and shut down Fluent once for all six tests.

The tests are:

1. Activate the species transport model
2. Check the command list
3. Create a custom mixture from custom species
4. Duplicate a mixture
5. Change the mixture assigned to a cellzone
6. Delete a mixture

The problem is that if one of these tests fails, all the following tests will fail as well, like dominoes. I'm not sure if this is acceptable. If it isn't, a potential solution is to implement recognizing an incremental test marker in our conftests.py file that would skip all remaining tests in the class if one fails: https://docs.pytest.org/en/latest/example/simple.html#incremental-testing-test-steps

[ansjsia]

@raph-luc @dnwillia-work I've recombined everything into one test in the latest commit. Hopefully the name and comments are sufficiently descriptive.

[ansjsia]

@dnwillia-work @raph-luc The unit testing check for 23R2 is stalling (timing out after 6 hours) consistently on the test test_meshing_workflow.py::test_watertight_workflow_children, which seems completely unrelated to this PR. It seems to fail when I run it locally on 23R2. Any insight?

[raph-luc]

@ansjsia I believe it wasn't test_watertight_workflow_children that stalled (as the logs say that it passed, and it should pass if you try it locally as well), it was the test after that one: test_watertight_workflow_dynamic_interface.

The team is aware of these tests that have been randomly stalling, we aren't sure of what is going on yet.

I set the failed test to re-run, let's see if it hangs again or if it passes. Changes in main branch are set to skip this test, we can merge them here if it fails again