Split the Flask-Login login manager initialization from the init_app method to the __init_login_manager method in the DigestAuth class, to simplify the code.

src/flask_digest_auth/auth.py

@@ -225,7 +225,7 @@ class DigestAuth:
         if opaque is not None:
             header += f", opaque=\"{opaque}\""
         if state.stale is not None:
-            header += f", stale=TRUE" if state.stale else f", stale=FALSE"
+            header += ", stale=TRUE" if state.stale else ", stale=FALSE"
         if self.algorithm is not None:
             header += f", algorithm=\"{self.algorithm}\""
         if len(self.__qop) > 0:
@@ -344,8 +344,15 @@ class DigestAuth:
             self.realm = app.config["DIGEST_AUTH_REALM"]
 
         if hasattr(app, "login_manager"):
-            from flask_login import LoginManager, login_user
+            self.__init_login_manager(app)
 
+    def __init_login_manager(self, app: Flask) -> None:
+        """Initializes the Flask-Login login manager.
+
+        :param app: The Flask application.
+        :return: None.
+        """
+        from flask_login import LoginManager, login_user
         login_manager: LoginManager = getattr(app, "login_manager")
 
         @login_manager.unauthorized_handler