feat!: Add methods for extracting data from fusion callers

[jarbesfeld]

closes #229

Some points:

• I updated one of the attributes in the Arriba class and added a new attribute for the Enfusion class
• For the new fixtures/ folder, I re-used the test datasets when applicable from here. For the fusion callers that did not have test data available, I either downloaded the one-row dataset from the fusion caller repos or created my own test one-row dataset
• It's possible the extraction methods could be refactored to remove some duplicate code

[jarbesfeld]

@korikuzma I moved the extraction methods directly into the fusion caller classes, so the extraction methods can be directly accessed from the classes