Add dedicated tests for external calculators, e.g. ALIGNN, CHGNet, etc. #15

• Maybe not here, but we will also want a real test for ALIGNN that makes sure things work, e.g. fullTest_ALIGNN which actually downloads the models, runs the calculations, and makes predictions against some references. Let's create a followup issue for this please.
• Let's rename this test_adapter_alignn.py to correctly indicate the scope.

Okay. I'll open an Issue to track this. I still don't know a good way how to do this on v0.6.0 though bc these adapters run on on different envs there. We can have them running on different actions, but we may need to keep them separatelly from the main crystALL suite of tests, as we can't run all of them in a single pytest run.

Running them in separate Actions should be perfectly fine I think. Just keep them in a separate directory like adapterTests and fire them individually instead of blanket pytest.

Originally posted by @amkrajewski in #10 (comment)