Remove unittest and switch to pytest fully

tests/conftest.py

@@ -0,0 +1,12 @@
+import pytest
+from auto_archiver.core.metadata import Metadata
+
+@pytest.fixture
+def make_item():
+    def _make_item(url: str, **kwargs) -> Metadata:
+        item = Metadata().set_url(url)
+        for key, value in kwargs.items():
+            item.set(key, value)
+        return item
+
+    return _make_item