Tests using physical simulations

[nichollsh]

We currently have tests using the Dummy simulations. This checks that the module coupling works okay and the dummy modules are working.

It is absolutely necessary to add tests for the physical modules. This PR introduces some initial tests for these, although they will surely be subject to change in the future. It runs PROTEUS with JANUS+Aragog+MORS+CALLIOPE for a few model steps. It does not run until convergence as this would take too long. Workflow runtime is about 5 minutes. Closes #237.

This increases the coverage from 45% to 59%. We could get this to ~65% if we included an AGNI test, but this would probably be quite slow.

Implementing these physical tests required adding installation steps for SOCRATES and Aragog to the CI workflow. These use caching to speed things up.

Includes a few bug fixes:

• Do not plot modern spectrum on Dummy stellar flux plots
• Do not try to copy the modern spectrum when using Dummy stellar model

GitHub records that a lot of files were changed, but most of these are changes to the test data. Apologies for the many random commits - it took some work to get the CI workflow working properly. The key thing with this is the order in which the modules are checked-out.

[nichollsh]

Yes I definitely agree. I think particularly once we have also looked into #193.

[nichollsh]

Thanks @lsoucasse!