Add testing suite

[rbdavid]

Add tests for implementation of the workflow as well as submodules' functions/classes. Ground-truth results can be pulled from previous versions of the ENA build code.

[rbdavid]

As part of #5, a basic pytest handle has been added. Need to add documentation for how to run these tests locally. Then expand to more aspects of the parse_embl.py functionality. Adding github actions would be good as well.