Add end-to-end test to compare model objects from 2023 to test outputs

Can add as unit test for `MakeGAMAbundance()` or as an end-to-end test (which I haven't drafted yet): Take system file with model outputs from 2023 review and write a unit test that compares a component of that model (e.g., the gcv) with the outcome from fitting the same model with the new functions inside the test. 