Refactor code structure for improved readability and maintainability

src/background/availability_checker.py

@@ -28,19 +28,19 @@ class AvailChecker(QThread):
             + str(links)
             + " with appnumber "
             + str(appnumber)
-            + "..."
+            + "...",
         )
         self.links = links
         self.appnumber = appnumber
         self.books = books or []
         log.info(
-            f"Started worker with appnumber: {self.appnumber} and links: {self.links} and {len(self.books)} books..."
+            f"Started worker with appnumber: {self.appnumber} and links: {self.links} and {len(self.books)} books...",
         )
         # Pre-create reusable request and transformer to avoid per-item overhead
         self._request = WebRequest().set_apparat(self.appnumber)
         self._rds_transformer = BibTextTransformer(TransformerType.RDS)
 
-    def run(self):
+    def run(self) -> None:
         self.db = Database()
         state = 0
         count = 0