tests (unit/conftests): Add a reset_storage autouse fixture:

Storage can be modified by tests, and it is kept for the whole session, this may have side
effect resulting in other tests failing. This fixture avoid this problem by reseting
`storage` between each test.

tests/unit/conftest.py

@@ -16,7 +16,6 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from contextlib import contextmanager
 from unittest.mock import MagicMock, AsyncMock
 from pytest import fixture
 from twisted.internet import defer
@@ -105,3 +104,14 @@ def client():
     client.tor = None
     client.tor_mode = TorMode.DISABLED
     return client
+
+
+@fixture(autouse=True)
+def reset_storage(host):
+    """Replace storage with a fresh mock before each test.
+
+    The host and storage fixtures use session scope, which means any assignments to
+    storage attributes (e.g., storage.method = AsyncMock(...)) persist across tests. This
+    fixture ensures each test starts with a clean slate.
+    """
+    host.memory.storage = AsyncMock()