Use pytest.mark.parametrize for IP4SCOUT test files

[dannywillems]

Problem

IP4SCOUT_FILES is discovered at module import time. If the test directory is missing or empty, the test loop body never executes and the test silently passes.

Proposal

Use pytest.mark.parametrize so each file is a distinct test case. Zero files becomes visible in test output instead of silently passing.

@pytest.mark.parametrize("path", IP4SCOUT_FILES, ids=lambda p: p.name)
def test_l9event_from_ip4scout(path):
    with open(path) as f:
        c = json.load(f)
    l9format.L9Event.from_dict(c)