refactor kpi calc tests to use singular constant fixtures for eligibility criteria shared across tests

[anchit-chandran]

All of the tests first start with setting eligibility criteria which are then passed into PatientFactory to create eligible patients.

E.g. in test_kpis_33_40.py:

@pytest.mark.django_db
def test_kpi_calculation_33(AUDIT_START_DATE):
   
...

    # Create  Patients and Visits that should be eligible (KPI5)
    eligible_criteria = {
        # KPI5 base criteria
        "visit__visit_date": AUDIT_START_DATE + relativedelta(days=2),
        "date_of_birth": AUDIT_START_DATE - relativedelta(days=365 * 10),
        # KPI 5 specific eligibility are any of the following:
        # Date of diagnosis NOT within the audit period
        "diagnosis_date": AUDIT_START_DATE - relativedelta(days=2),
        # Date of leaving service NOT within the audit period
        # transfer date only not None if they have left
        "transfer__date_leaving_service": None,
        # Date of death NOT within the audit period"
        "death_date": None,
    }

Often, these eligibility criteria are based on the same measures, usually KPI 1, 5, 6 so far. I think the eligibility criteria may require tweaking so rather than defining them individually in each test as this will be a nightmare to tweak, refactor all universal ones into conftest.py (so all tests can globally access them) as fixtures. An example already exists in conftest.py with AUDIT_START_DATE:

@pytest.fixture
def AUDIT_START_DATE():
    """AUDIT_START_DATE is Day 2 of the first audit period"""
    return date(year=2024, month=4, day=1)

Which can then be used in any test (passing into the test function as an argument) without import e.g in test_kpis_33_40.py:

@pytest.mark.django_db
def test_kpi_calculation_33(AUDIT_START_DATE):
    """Tests that KPI33 is calculated correctly.

    Calculates KPI 32: HbA1c 4+ (%)

    Numerator: Number of eligible patients with at least four entries for HbA1c value (item 17) with an observation date (item 19) within the audit period

    Denominator: Number of patients with Type 1 diabetes with a complete year of care in the audit period (measure 5)
    """

    # Ensure starting with clean pts in test db
    Patient.objects.all().delete()

    # Create  Patients and Visits that should be eligible (KPI5)
    eligible_criteria = {
        # KPI5 base criteria
        "visit__visit_date": AUDIT_START_DATE + relativedelta(days=2),