objstorage_checker: Use check method from object storage interface

Instead of reinventing the wheel, prefer to use the check method from the object storage interface for verifying content presence and integrity.

Depends on !65 (merged) and swh-objstorage!178 (merged).

Related to #4694 (closed).

swh/scrubber/tests/conftest.py

-# Copyright (C) 2022  The Software Heritage developers
+# Copyright (C) 2022-2024  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -12,6 +12,7 @@ from pytest_postgresql import factories
 
 from swh.core.db.db_utils import initialize_database_for_module
 from swh.journal.serializers import value_to_kafka
+from swh.journal.writer import get_journal_writer
 from swh.model.hashutil import hash_to_bytes
 from swh.model.model import Directory, DirectoryEntry
 from swh.model.swhids import ObjectType
@@ -110,3 +111,27 @@ def corrupt_object(scrubber_db, config_entry):
         first_occurrence=datetime.datetime.now(tz=datetime.timezone.utc),
         object_=value_to_kafka(CORRUPT_DIRECTORY.to_dict()),
     )
+
+
+@pytest.fixture
+def journal_client_config(
+    kafka_server: str, kafka_prefix: str, kafka_consumer_group: str
+):
+    return dict(
+        cls="kafka",
+        brokers=kafka_server,
+        group_id=kafka_consumer_group,
+        prefix=kafka_prefix,
+        on_eof="stop",
+    )
+
+
+@pytest.fixture
+def journal_writer(kafka_server: str, kafka_prefix: str):
+    return get_journal_writer(
+        cls="kafka",
+        brokers=[kafka_server],
+        client_id="kafka_writer",
+        prefix=kafka_prefix,
+        anonymize=False,
+    )