**Replace Flake8 with Ruff, refactor type hints, and enhance archive processing logic**

- Removed `flake8` and `flake8-annotations` from dependencies, replaced by `ruff` for linting.
- Introduced cleaner type hinting and modern Python annotations (PEP 604 style) across multiple modules.
- Moved archive processing to a dedicated helper (`comic.archives`) for improved maintainability.
- Updated and simplified logic for archive file retrieval, directory cleaning, and user access validation.
- Improved error handling and added support for user classification restrictions in API responses.

comic/tests/conftest.py

@@ -0,0 +1,48 @@
+"""Shared fixtures for the test suite."""
+
+from pathlib import Path
+
+import pytest
+
+from comic import models
+from comic.tests.factories import make_cbz
+
+
+@pytest.fixture()
+def comic_volume(settings, tmp_path) -> Path:
+    """Point COMIC_BOOK_VOLUME at an empty temporary directory."""
+    settings.COMIC_BOOK_VOLUME = tmp_path
+    return tmp_path
+
+
+@pytest.fixture()
+def admin_user(db) -> models.User:
+    return models.User.objects.create_superuser('admin', 'admin@example.com', 'password12345')
+
+
+@pytest.fixture()
+def reader_user(db) -> models.User:
+    """A normal user, whose reading allowance defaults to the highest rating."""
+    return models.User.objects.create_user('reader', 'reader@example.com', 'password12345')
+
+
+@pytest.fixture()
+def restricted_user(db) -> models.User:
+    """A user whose allowance is G, so anything rated above G is blocked."""
+    user = models.User.objects.create_user('restricted', 'restricted@example.com', 'password12345')
+    models.UserMisc.objects.create(user=user, allowed_to_read=models.Directory.Classification.C_G)
+    return user
+
+
+@pytest.fixture()
+def rated_directory(db) -> models.Directory:
+    return models.Directory.objects.create(name='Rated', classification=models.Directory.Classification.C_18)
+
+
+@pytest.fixture()
+def book(db, comic_volume: Path, rated_directory: models.Directory) -> models.ComicBook:
+    """A book with a three page archive inside an 18 rated directory."""
+    directory_path = comic_volume / rated_directory.name
+    directory_path.mkdir(parents=True, exist_ok=True)
+    make_cbz(directory_path / 'issue.cbz', pages=3)
+    return models.ComicBook.objects.create(file_name='issue.cbz', directory=rated_directory, page_count=3)