Thermodynamics integration test

Fixes #499

Task List

[ ] Defined the tests that specify a complete and functioning change (It may help to create a design specification & test specification)
[ ] Implemented the source code change that satisfies the tests
[ ] Documented the feature by providing worked example
[ ] Updated the README or other documentation
[ ] Completed the pre-Request checklist below

Change Description

Add an integration test which runs the full model in a single-column mode and tests the outputs against known good values.

The model setup should roughly reproduce the results of papers such as Maykut and Untersteiner (1971), Semtner (1976), and Winton (2000).

Test Description

The test in test/ThermoIntegration_test.py creates an initialisation file and config file, runs the model, and compares the output against some known good values.

Documentation Impact

Documentation of this and other idealised tests is tracked in issue #520

Other Details

N/A

Pre-Request Checklist

[ ] The requirements of this pull request are fully captured in an issue or design specification and are linked and summarised in the description of this PR
[ ] No new warnings are generated
[ ] The documentation has been updated (or an issue has been created to track the corresponding change)
[ ] Methods and Tests are commented such that they can be understood without having to obtain additional context
[ ] This PR/Issue is labelled as a bug/feature/enhancement/breaking change
[ ] File dates have been updated to reflect modification date
[ ] This change conforms to the conventions described in the README

nextsimhub / nextsimdg

Thermodynamics integration test #521