Fix tests: add data_transfer_bytes to expected API responses

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Andrey Cheptsov

src/dstack/_internal/server/services/instances.py

@@ -241,7 +241,7 @@ def instance_model_to_instance(instance_model: InstanceModel) -> Instance:
         finished_at=instance_model.finished_at,
         total_blocks=instance_model.total_blocks,
         busy_blocks=instance_model.busy_blocks,
-        data_transfer_bytes=instance_model.data_transfer_bytes,
+        data_transfer_bytes=instance_model.data_transfer_bytes or 0,
     )
 
     offer = get_instance_offer(instance_model)

src/tests/_internal/server/routers/test_fleets.py

@@ -963,6 +963,7 @@ async def test_creates_fleet(self, test_db, session: AsyncSession, client: Async
                     "price": None,
                     "total_blocks": 1,
                     "busy_blocks": 0,
+                    "data_transfer_bytes": 0,
                 }
             ],
         }
@@ -1105,6 +1106,7 @@ async def test_creates_ssh_fleet(self, test_db, session: AsyncSession, client: A
                     "price": 0.0,
                     "total_blocks": 1,
                     "busy_blocks": 0,
+                    "data_transfer_bytes": 0,
                 }
             ],
         }
@@ -1285,6 +1287,7 @@ async def test_updates_ssh_fleet(self, test_db, session: AsyncSession, client: A
                     "price": 0.0,
                     "total_blocks": 1,
                     "busy_blocks": 0,
+                    "data_transfer_bytes": 0,
                 },
                 {
                     "id": SomeUUID4Str(),
@@ -1320,6 +1323,7 @@ async def test_updates_ssh_fleet(self, test_db, session: AsyncSession, client: A
                     "price": 0.0,
                     "total_blocks": 1,
                     "busy_blocks": 0,
+                    "data_transfer_bytes": 0,
                 },
             ],
         }