Pytest QOL improvements

[CBroz1]

1. Currently, the full suite of pytests is very time consuming (taking over an hour), as we insert and delete between each test. By adding fixture scope, we could reduce this time significantly.

@pytest.fixture(scope="session")
def ingest_subjects(pipeline, subjects_csv):
    pass # keep as is

2. Currently, there are DuplicateErrors if _tear_down=False. By adding skip_duplicates to insert functions or pytest markers (e.g., skipif or xfail), we could make better use of non-teardown iterations.